13 October 2026 Current Affairs: Headlines, GK & MCQs

The correct answer is A, 1 only. Under First-Past-the-Post a candidate needs only more votes than any rival, not a majority, while Proportional Representation does not require a winner to secure a majority either.

In the First-Past-the-Post (simple plurality) system, used for Lok Sabha and Vidhan Sabha elections in India, the candidate with the highest number of votes wins. When several candidates contest, the winner often polls well under half of the votes cast, so statement 1 is correct. Under Proportional Representation, seats are shared in proportion to votes, or a candidate wins by reaching a quota under the single transferable vote, as in Rajya Sabha and presidential elections. A quota is usually far below a majority, so statement 2 is wrong.

B is wrong: statement 2 is incorrect, because PR rewards a share of votes or a quota, not a majority.

C is wrong: only statement 1 holds.

D is wrong: statement 1 correctly describes how plurality voting works.

Exam tip: FPTP = most votes wins (plurality); PR with single transferable vote = Rajya Sabha, President and Vice-President elections.

The correct answer is A, Chess skills. Chess skill is an acquired trait, built by learning and practice, and acquired traits are not passed on through genes.

Only inherited traits, which are coded in the DNA of the reproductive cells, reach the next generation. Skills, knowledge, a trained body or a scar change the body cells of one person but leave the genes in the sperm or egg untouched, so the child does not receive them. This is why Lamarck's idea of inheritance of acquired characters was rejected and Weismann's germ plasm theory accepted. Hair texture, the type of earlobe and freckles are controlled by genes, so a child can inherit them.

B is wrong: curly hair is a genetic trait that can be inherited.

C is wrong: attached or free earlobes is a classic inherited trait used in genetics lessons.

D is wrong: freckles are largely determined by genes and run in families.

Exam tip: acquired traits (skills, muscles, injuries) are not inherited; genetic traits (eye colour, earlobes, hair type) are.

The correct answer is C, Both 1 and 2. C. Rajagopalachari is listed first among the first Bharat Ratna awardees of 1954, and Deen Dayal Upadhyaya gave the philosophy of Integral Humanism.

The Bharat Ratna, India's highest civilian honour, was instituted in 1954. The first three recipients that year were C. Rajagopalachari, the last Governor-General of India, the philosopher Sarvepalli Radhakrishnan and the physicist C. V. Raman, with Rajagopalachari named first. Deen Dayal Upadhyaya, a leader of the Bharatiya Jana Sangh, presented Integral Humanism (Ekatma Manavvad) in a series of lectures in 1965. It sees the individual, society and nature as one whole and offers an Indian alternative to both capitalism and communism.

A is wrong: statement 2 is also correct.

B is wrong: statement 1 is also correct.

D is wrong: both statements are true.

Exam tip: Bharat Ratna 1954 = Rajagopalachari, Radhakrishnan, C. V. Raman; Integral Humanism = Deen Dayal Upadhyaya, 1965.

The correct answer is B, Cumulus. Cumulus clouds look like heaps of cotton wool, appear in scattered patches with a flat base, and generally form at a height of 4 to 7 km.

Clouds are grouped by shape and height into four basic forms: cirrus, cumulus, stratus and nimbus. Cumulus clouds grow when warm air rises by convection, so they build upward into puffy, rounded tops while their base stays flat at the level where the rising air condenses. They are common on fine summer days. When a cumulus cloud keeps growing it can turn into a towering cumulonimbus that brings thunderstorms.

A is wrong: cirrus clouds form very high, at 8 to 12 km, and are thin, wispy and feathery.

C is wrong: nimbus clouds are dark, thick rain clouds that form low and have no cotton-wool look.

D is wrong: stratus clouds are layered sheets that cover large parts of the sky, not separate patches.

Exam tip: cirrus = feathery and highest, cumulus = cotton wool with flat base, stratus = layers, nimbus = dark rain clouds.

The correct answer is D, Endodermis. The endodermis is the innermost layer of the cortex that surrounds the vascular tissue; it is not a part of the vascular bundle itself.

A vascular bundle is the conducting strand of a plant. It is made of xylem, which carries water and minerals upward from the roots, and phloem, which carries food made in the leaves to other parts. In dicot stems a strip of cambium lies between xylem and phloem; such open bundles can produce new tissue and help the stem grow thicker. The endodermis, a single layer of barrel-shaped cells with the Casparian strip in roots, sits outside the stele and controls the entry of water into it.

A is wrong: phloem is one of the two conducting tissues of every vascular bundle.

B is wrong: xylem is the water-conducting part of the vascular bundle.

C is wrong: cambium lies within the open vascular bundles of dicots, between xylem and phloem.

Exam tip: vascular bundle = xylem + phloem (+ cambium if open); endodermis with Casparian strip lies outside it.

The correct answer is C, Panna. Panna in Bundelkhand, now in Madhya Pradesh, is India's historic diamond belt, and diamonds were mined there in the medieval period.

The diamond-bearing rocks of the Vindhyan range around Panna have yielded gems for centuries, and the town later became famous under the Bundela ruler Chhatrasal. Panna remains the only area in India where diamonds are still mined, at the Majhgawan mine run by the National Mineral Development Corporation. The other great medieval source was the Golconda region of the Deccan, whose mines along the Krishna gave the world famous stones such as the Koh-i-Noor.

A is wrong: Awadh was a fertile agricultural province of the Gangetic plain, not a mining area.

B is wrong: Khambhat (Cambay) in Gujarat was a great sea port for textiles and trade, not a mine.

D is wrong: Lakhnauti (Gaur) was the capital of the Bengal province, known for rice and textiles.

Exam tip: diamonds in Indian history = Panna (Bundelkhand) and Golconda (Deccan); Khambhat = port of Gujarat.

The correct answer is A, ventricular contraction and ventricular relaxation, respectively. 120 mmHg is the systolic pressure when the ventricles contract, and 80 mmHg is the diastolic pressure when they relax.

Blood pressure is the force of blood on the walls of the arteries and is measured with a sphygmomanometer. When the ventricles contract (systole), they push blood into the aorta and the pressure rises to its peak, about 120 mmHg in a healthy adult. When the ventricles relax and refill (diastole), the pressure in the arteries falls to its lowest, about 80 mmHg. A reading that stays at or above 140/90 mmHg is treated as high blood pressure, or hypertension.

B is wrong: it reverses the order; the higher number is the contraction reading.

C is wrong: the readings are taken from arteries and reflect the ventricles, not the auricles (atria).

D is wrong: the lower number is ventricular relaxation, not auricular contraction.

Exam tip: systolic 120 = ventricles contract; diastolic 80 = ventricles relax; measured with a sphygmomanometer.

The correct answer is B, NBFCs cannot give loans. This statement is false, because lending and advancing loans is the main business of most NBFCs.

A Non-Banking Financial Company is a company registered under the Companies Act whose principal business is loans and advances, buying shares and securities, leasing, hire-purchase, insurance or chit funds. NBFCs are regulated by the Reserve Bank of India and do work similar to banks, but they hold no banking licence. The RBI therefore marks three differences: an NBFC cannot accept demand deposits, it is not part of the payment and settlement system so it cannot issue cheques drawn on itself, and its depositors do not get the deposit insurance cover of DICGC.

A is wrong as an answer: it is a correct statement; NBFCs cannot take demand deposits.

C is wrong as an answer: it is correct; NBFCs cannot issue cheques on themselves.

D is wrong as an answer: it is correct; DICGC insurance covers bank deposits, not NBFC deposits.

Exam tip: NBFC vs bank = no demand deposits, no cheques on itself, no DICGC cover; lending is allowed.

The correct answer is C, The force would be halved. Doubling one mass doubles the force, while doubling the distance cuts it to one-fourth, so the net result is 2 × 1/4 = 1/2.

Newton's law of universal gravitation states that F = G m1 m2 / r², where G is the universal gravitational constant. The force is directly proportional to the product of the two masses and inversely proportional to the square of the distance between their centres. Because distance enters as a square, changing it has a much larger effect than changing a mass by the same factor. Here the new force is G (2m1) m2 / (2r)² = (2/4) F = F/2.

A is wrong: the two changes do not cancel, since the distance effect is squared.

B is wrong: that would happen only if the distance stayed the same.

D is wrong: the force falls; it would rise four times only if the distance were halved.

Exam tip: F ∝ m1 m2 / r²; double r and F becomes one-fourth, halve r and F becomes four times.

The correct answer is B, Pb and Sn. Common solder is an alloy of lead (Pb) and tin (Sn), often in a ratio close to 40:60.

Solder is used to join metal parts, especially wires and components in electrical circuits. The useful property of the lead-tin alloy is its low melting point, around 183 °C for the eutectic mix, which is lower than that of either pure metal. This lets it melt with a soldering iron and set quickly without damaging the parts it joins. Because lead is toxic, lead-free solders made mainly of tin with small amounts of silver and copper are now widely used in electronics.

A is wrong: lead and zinc do not make solder; zinc is used in brass and in galvanising.

C is wrong: silicon is a semiconductor and is not alloyed with lead for solder.

D is wrong: cobalt is used in magnets and superalloys, not in solder.

Exam tip: solder = lead + tin; brass = copper + zinc; bronze = copper + tin.

The correct answer is D, The Congress agreed to take part in the Second Round Table Conference. Under the pact, signed on 5 March 1931, Congress agreed to attend the next conference in London, and Gandhi went as its sole representative.

The Gandhi-Irwin Pact ended the first phase of the Civil Disobedience Movement that began with the Dandi March of 1930. The Viceroy Lord Irwin agreed to release political prisoners not convicted of violence, to return confiscated property not yet sold, to allow peaceful picketing of liquor and foreign cloth shops, and to permit people near the coast to make salt for their own use. In return Congress suspended the movement. The Karachi session of March 1931 endorsed the pact.

A is wrong: the Government agreed to release prisoners who had been non-violent.

B is wrong: peaceful picketing was allowed, and such prisoners were released.

C is wrong: Congress did agree to suspend the Civil Disobedience Movement.

Exam tip: Gandhi-Irwin Pact, 5 March 1931 = movement suspended, Second Round Table Conference attended, Karachi session endorsed it.

The correct answer is A, frequency. Pitch is how high or low a sound seems to the ear, and it depends on the frequency of vibration: the higher the frequency, the higher the pitch.

Frequency is the number of vibrations a source makes per second and is measured in hertz (Hz). A whistle or a child's voice vibrates fast and sounds shrill, while a drum or a lion's roar vibrates slowly and sounds deep. Women usually have a higher-pitched voice than men because their vocal cords are shorter and vibrate faster. The human ear hears roughly 20 Hz to 20,000 Hz; below that range is infrasound and above it is ultrasound.

B is wrong: amplitude decides the loudness of a sound, not its pitch.

C is wrong: wavelength changes with the medium for the same note; pitch is set by frequency.

D is wrong: intensity is the energy carried per unit area and relates to loudness.

Exam tip: pitch = frequency, loudness = amplitude, quality (timbre) = waveform.

The correct answer is B, Loan bonds signed between money-lender and Ryots would have validity only for three years. The Limitation Law of 1859 was meant to stop debts from piling up over many years.

In the Deccan, ryots borrowed from moneylenders (sahukars) and signed bonds. The British passed the Limitation Law in 1859 so that such a bond would lapse after three years, hoping to check the endless growth of interest. Moneylenders got round it by making ryots sign a fresh bond every three years, adding the unpaid interest to the principal. Anger over such debts fed the Deccan Riots of 1875, when ryots attacked sahukars and burnt their account books. The Deccan Agriculturists' Relief Act followed in 1879.

A is wrong: the law did not cancel loan bonds; it limited how long they stayed valid.

C is wrong: the law said nothing about moneylenders being barred from executing bonds.

D is wrong: the period of validity was three years, not ten.

Exam tip: Limitation Law 1859 = loan bonds valid three years; Deccan Riots 1875; Deccan Agriculturists' Relief Act 1879.

The correct answer is A, Magnesium and hydrochloric acid. Magnesium is above hydrogen in the reactivity series, so it displaces hydrogen from the acid: Mg + 2HCl → MgCl2 + H2.

Metals that are more reactive than hydrogen, such as magnesium, zinc and iron, release hydrogen gas when they react with dilute hydrochloric or sulphuric acid, forming a salt. The gas can be identified because it burns with a pop sound when a lit splinter is brought near. Nitric acid behaves differently: it is a strong oxidising agent, so it oxidises the hydrogen produced to water and itself is reduced to oxides of nitrogen. Only very dilute nitric acid gives hydrogen with magnesium or manganese.

B is wrong: copper is below hydrogen and does not displace it; with nitric acid it gives nitric oxide.

C is wrong: a carbonate reacts with acid to give carbon dioxide, not hydrogen.

D is wrong: nitric acid oxidises the hydrogen, so zinc gives oxides of nitrogen instead.

Exam tip: metal + dilute HCl or H2SO4 = salt + hydrogen (pop test); carbonate + acid = CO2; nitric acid usually gives no hydrogen.

The correct answer is A, To increase the life of the bulb. Argon is an inert gas, so it does not react with the white-hot tungsten filament and slows its evaporation, which makes the bulb last longer.

In an incandescent bulb the tungsten filament glows at well over 2,500 °C. In air it would burn up at once by reacting with oxygen, and even in a vacuum the hot tungsten slowly evaporates, thins and blackens the glass. Filling the bulb with a chemically inactive gas such as argon, often mixed with some nitrogen, prevents oxidation and presses back on the escaping tungsten atoms. Tungsten itself is chosen for its very high melting point of about 3,400 °C.

B is wrong: argon does not reduce power use; the filament's resistance and rating decide that.

C is wrong: the bulb still gives ordinary white-yellow light; argon is not there for colour.

D is wrong: argon is added for durability, not to cut the cost of making the bulb.

Exam tip: bulb filament = tungsten (very high melting point); filled gas = argon or nitrogen (inert) to protect it.

The correct answer is B, transfusion of contaminated blood and blood products. HIV spreads through body fluids such as blood, so a transfusion of infected blood passes the virus directly into the bloodstream.

HIV attacks the helper T-cells (CD4 cells) of the immune system, and over years the body loses its power to fight infections; this late stage is AIDS. The virus is carried in blood, semen, vaginal fluids and breast milk. It is transmitted by unprotected sexual contact, by sharing infected needles and syringes, by transfusion of untested blood, and from an infected mother to her child during pregnancy, birth or breastfeeding. ELISA is the usual screening test, which is why all donated blood is tested before use.

A is wrong: HIV does not spread through food or water; that is how cholera or typhoid spread.

C is wrong: HIV is not an airborne virus like influenza or tuberculosis bacteria.

D is wrong: casual contact such as shaking hands or hugging does not transmit HIV.

Exam tip: HIV spreads by blood, sex, shared needles and mother to child; it attacks CD4 helper T-cells; test = ELISA.

The correct answer is C, Thermal power plants. Coal-based thermal plants produce the largest share of India's electricity, roughly three-fourths of the power generated.

A thermal power plant burns a fuel, mostly coal and to a smaller extent gas or lignite, to boil water into steam that turns a turbine. India has large coal reserves in Jharkhand, Odisha, Chhattisgarh and West Bengal, which is why most big thermal stations lie in or near the coalfields or are linked to them by rail. NTPC is the largest power producer in the country. Renewable sources such as solar and wind are growing fast, but coal-fired generation still leads by a wide margin.

A is wrong: hydropower gives only around a tenth of India's electricity.

B is wrong: nuclear plants supply only about three per cent of the country's power.

D is wrong: wind is a growing renewable source but far behind thermal power in generation.

Exam tip: India's electricity mix = thermal (coal) first, then renewables and hydro, with nuclear smallest.

The correct answer is C, 1 and 3 only. The merger was made by an Act of Parliament and the Bombay High Court still has jurisdiction, but the merged UT has two Lok Sabha seats, not three.

The Dadra and Nagar Haveli and Daman and Diu (Merger of Union Territories) Act, 2019 joined the two Union Territories into one with effect from 26 January 2020, with Daman as its capital. Under Article 3 and Article 4, Parliament can form or alter units by law, which is how the merger was done. The Act kept the two existing seats in the House of the People, one for Dadra and Nagar Haveli and one for Daman and Diu. It also continued the jurisdiction of the High Court of Bombay over the whole UT.

A is wrong: statement 2 is false, since only two seats were allotted.

B is wrong: it includes the false statement 2 and leaves out the true statement 1.

D is wrong: statement 2 alone is the incorrect one.

Exam tip: DNH and DD merged on 26 January 2020 by a 2019 Act; capital Daman, 2 Lok Sabha seats, Bombay High Court.

The correct answer is A, Left atrium. The pulmonary veins bring oxygen-rich blood from the lungs straight into the left atrium.

The human heart has four chambers and works as two pumps. The right side handles deoxygenated blood: the right atrium receives it from the body through the venae cavae and the right ventricle sends it to the lungs through the pulmonary artery. In the lungs the blood picks up oxygen and returns through the four pulmonary veins to the left atrium. From there it passes through the bicuspid (mitral) valve into the left ventricle, the thickest-walled chamber, which pumps it into the aorta for the whole body.

B is wrong: the right atrium receives deoxygenated blood from the body.

C is wrong: the left ventricle receives oxygenated blood only after the left atrium, then pumps it to the body.

D is wrong: the right ventricle pumps deoxygenated blood to the lungs.

Exam tip: pulmonary veins carry oxygenated blood to the left atrium; the pulmonary artery carries deoxygenated blood to the lungs.

The correct answer is C, Both 1 and 2. Erok Sim is a sowing festival of the Santhals, and Sangken is the Buddhist new-year water festival of Arunachal Pradesh.

The Santhals, one of India's largest tribal communities, live mainly in Jharkhand, West Bengal, Odisha and Bihar, and their festivals follow the farming year. Erok Sim marks the sowing of seeds, while Sohrai is their harvest festival after the crops are gathered. Sangken is celebrated in mid-April by the Theravada Buddhist Khampti and Singpho communities of Namsai and nearby areas of Arunachal Pradesh. Images of the Buddha are bathed and people sprinkle water on one another, much like Songkran in Thailand and Thingyan in Myanmar.

A is wrong: statement 2 is also correct.

B is wrong: statement 1 is also correct.

D is wrong: both statements are true.

Exam tip: Santhal festivals = Erok Sim (sowing), Sohrai (harvest); Sangken = Khampti Buddhist water festival of Arunachal.

The correct answer is D, Tropical wet and dry climate. This is the savanna (Sudan type) climate: hot all year, with a short rainy summer and a long dry season.

The tropical wet and dry climate, marked Aw in the Köppen scheme, lies between the equatorial rainforest belt and the hot deserts, roughly 5° to 20° on either side of the equator. Rain comes in the hot season when the overhead sun draws the rain belt in, and the rest of the year is dry. The natural vegetation is tall grass with scattered trees, the savanna. The Sudan region of Africa, the Campos of Brazil and the Gran Chaco around Paraguay are typical examples.

A is wrong: a sub-tropical steppe is semi-arid with very little rain and cooler winters.

B is wrong: a mid-latitude steppe, such as the Prairies, has hot summers and cold winters, not heat all year.

C is wrong: a tropical monsoon climate gets heavy rain from seasonal winds and is not the Sudan type.

Exam tip: savanna = tropical wet and dry = Sudan type; equatorial = rain all year; steppe = semi-arid grassland.

The correct answer is B, Sea water. Dissolved salts make sea water less compressible, so sound travels faster in it, about 1,530 m/s at 25 °C, than in pure or drinking water.

The speed of sound in a medium depends on its elasticity (how strongly it resists compression) compared with its density. Salt raises the bulk modulus of water more than it raises the density, so the speed goes up with salinity. That is why sound is fastest in sea water among these liquids. Distilled water carries sound at about 1,498 m/s at 25 °C, and drinking water, with only a little dissolved mineral, is very close to that. In general sound travels fastest in solids, then liquids, and slowest in gases.

A is wrong: distilled water has no dissolved salts, so sound is slower in it than in sea water.

C is wrong: drinking water has only small amounts of minerals, so its speed is close to that of pure water.

D is wrong: methanol is much more compressible, and sound travels at only about 1,100 m/s in it.

Exam tip: speed of sound: solids > liquids > gases; sea water > fresh water; it rises with temperature.

The correct answer is A, It orbits the Sun, about 15 lakh km away from the Earth. The telescope sits near the second Lagrange point (L2), about 1.5 million km from Earth, and goes round the Sun along with the Earth.

The James Webb Space Telescope, built by NASA with the European and Canadian space agencies, was launched on 25 December 2021 on an Ariane 5 rocket from French Guiana. It observes mainly in infrared light to study the earliest galaxies, the birth of stars and the atmospheres of exoplanets. At L2, on the side of the Earth away from the Sun, the pull of the Sun and the Earth together lets it keep pace with the Earth's yearly orbit. A large sunshield keeps its gold-coated mirror, 6.5 m wide, very cold.

B is wrong: it does not orbit the Earth; at L2 it moves around the Sun.

C is wrong: it is not stationary, and its distance is about 15 lakh km, not 10 lakh km.

D is wrong: it does not revolve around the Moon, which is only about 3.84 lakh km away.

Exam tip: JWST = launched 25 Dec 2021, infrared, L2 point about 1.5 million km away, successor to Hubble.

The correct answer is D, Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l). Slaked lime is calcium hydroxide applied as a watery solution, and it takes up carbon dioxide gas from the air to form solid calcium carbonate and water.

Whitewash is made by adding water to quicklime (calcium oxide), a strongly exothermic reaction that gives slaked lime: CaO + H2O → Ca(OH)2. A solution of this slaked lime is painted on the walls. Over two or three days it reacts with carbon dioxide in the air and leaves a thin, hard layer of calcium carbonate, which gives the walls their shiny white finish. Calcium carbonate is the same compound found in limestone, chalk and marble.

A is wrong: it starts from quicklime (CaO), not slaked lime.

B is wrong: it uses quicklime and wrongly shows it as a liquid.

C is wrong: slaked lime is applied as an aqueous solution and carbon dioxide reacts as a gas, so the physical states are wrong.

Exam tip: quicklime CaO + water = slaked lime Ca(OH)2; slaked lime + CO2 = CaCO3, the shiny whitewash layer.

The correct answer is D, 850 m. The sound travels to the cliff and back in 5 s, so it covers 340 × 5 = 1,700 m in all, and the cliff is half of that, 850 m away.

An echo is a reflected sound heard separately from the original. Since the sound makes a round trip, the distance to the reflecting surface is d = (speed × time) / 2. Here d = (340 × 5) / 2 = 850 m. The human ear keeps a sound in memory for about 0.1 second, so to hear a distinct echo in air at 344 m/s the reflecting surface must be at least about 17.2 m away. The same principle is used in SONAR to find the depth of the sea and in bats' echolocation.

A is wrong: 1,700 m is the total path to the cliff and back, not the distance to the cliff.

B is wrong: 170 m would give an echo after only 1 second.

C is wrong: 85 m would give an echo after only half a second.

Exam tip: echo distance = speed × time ÷ 2; minimum distance for a clear echo is about 17 m.

The correct answer is C, Rubber products. Rubber products are not among the Eight Core Industries tracked by the Index of Eight Core Industries.

The Index of Eight Core Industries measures the output of the key infrastructure sectors every month and is released by the Office of the Economic Adviser in DPIIT, under the Ministry of Commerce and Industry. The eight industries are coal, crude oil, natural gas, refinery products, fertilizers, steel, cement and electricity. On the 2011-12 base they carry a combined weight of about 40.27 per cent in the Index of Industrial Production. Refinery products have the largest weight among them, followed by electricity and steel, while fertilizers have the smallest.

A is wrong as an answer: coal is one of the eight core industries.

B is wrong as an answer: refinery products are a core industry and carry the highest weight.

D is wrong as an answer: cement is one of the eight core industries.

Exam tip: eight core industries = coal, crude oil, natural gas, refinery products, fertilizers, steel, cement, electricity; refinery products weigh most.

The correct answer is B, A white substance is formed when an aqueous solution of barium chloride is mixed with sodium sulphate solution. This is a double displacement (precipitation) reaction, in which no element gains oxygen or loses electrons.

When the two solutions are mixed, the ions swap partners: BaCl2 + Na2SO4 → BaSO4 + 2NaCl. Barium sulphate is insoluble in water, so it separates out as a white precipitate, while sodium chloride stays dissolved. The oxidation number of every element stays the same, so it is not a redox change. The other three are everyday examples of oxidation by the oxygen in air, which NCERT also uses to explain rancidity and corrosion.

A is wrong as an answer: butter turns rancid because its fats and oils are oxidised by air.

C is wrong as an answer: the reddish-brown rust on iron is hydrated iron(III) oxide, formed by oxidation.

D is wrong as an answer: wine turns sour when its ethanol is oxidised to acetic acid.

Exam tip: BaCl2 + Na2SO4 = white BaSO4 precipitate, a double displacement; rancidity, rusting and souring of wine are oxidation.

The correct answer is C, Decrease in the available energy at higher trophic levels. Energy shrinks sharply at each step of a food chain, so after a few levels too little is left to support another level of consumers.

Energy flows one way through an ecosystem, from the Sun to producers and then to herbivores and carnivores. Raymond Lindeman's ten per cent law says only about 10 per cent of the energy at one trophic level reaches the next; the rest is used in respiration and lost as heat. If plants hold 10,000 units of energy, herbivores get about 1,000, primary carnivores 100 and secondary carnivores only 10. This is why most food chains have only three or four, rarely five, trophic levels, and why the pyramid of energy is always upright.

A is wrong: food supply varies locally, but the basic limit is the loss of energy between levels.

B is wrong: air pollution does not set the number of trophic levels.

D is wrong: parasites are part of food chains but do not decide how long they can be.

Exam tip: ten per cent law (Lindeman) = only 10% energy passes to the next level; pyramid of energy is always upright.

The correct answer is D, Amritlal Vithaldas Thakkar. A. V. Thakkar, known as Thakkar Bapa, founded the Bhil Seva Mandal in 1922 to work for the Bhil tribals of the Panchmahal district of Gujarat.

Thakkar Bapa was an engineer who left his career to serve the poorest communities. He worked with the Servants of India Society of Gopal Krishna Gokhale and became a close associate of Mahatma Gandhi. Through the Bhil Seva Mandal he ran schools, hostels and welfare work among the Bhils. He later served as general secretary of the Harijan Sevak Sangh, founded in 1932, and after independence he was a member of the Constituent Assembly, where he chaired a sub-committee on the excluded and partially excluded tribal areas.

A is wrong: Dayaram Gidumal was a Sindhi social reformer who co-founded the Seva Sadan with Behramji Malabari.

B is wrong: Gurusaday Dutt founded the Bratachari movement to revive Bengal's folk arts.

C is wrong: D. K. Karve worked for women's education and widow remarriage and founded SNDT Women's University.

Exam tip: Thakkar Bapa = Bhil Seva Mandal (1922), Harijan Sevak Sangh; Karve = women's university; Gurusaday Dutt = Bratachari.

The correct answer is B, Leh. Leh lies in the rain shadow of the Great Himalaya and gets only about 100 mm of precipitation a year, making it one of the driest places in India.

Leh, in the Union Territory of Ladakh, is a cold desert at about 3,500 m above sea level. The monsoon winds shed almost all their moisture on the southern slopes of the Himalaya and the Pir Panjal, so very little reaches the Indus valley beyond them. Most of Leh's meagre precipitation comes as light snow in winter from western disturbances. The thin air, strong sunshine and very low humidity give Ladakh its bare, brown landscape.

A is wrong: Jodhpur in the Thar region is dry but receives roughly 350-400 mm of rain a year.

C is wrong: New Delhi gets about 700-800 mm, mostly from the south-west monsoon.

D is wrong: Bengaluru receives about 900 mm or more from both monsoons.

Exam tip: driest areas of India = Leh (cold desert) and western Rajasthan (hot desert); wettest = Mawsynram and Cherrapunji.

The correct answer is A, They are deflected by electric fields. X-rays are electromagnetic waves with no electric charge, so electric fields cannot deflect them.

X-rays were discovered by Wilhelm Röntgen in 1895, who won the first Nobel Prize in Physics in 1901 for it. They are produced when fast electrons strike a metal target and have wavelengths of roughly 0.01 to 10 nanometres, thousands of times shorter than visible light at 400-700 nm. Being high-energy photons, they pass through soft tissue but are absorbed by dense bone, which is why they are used to image fractures. Like all electromagnetic waves they travel at the speed of light and are unaffected by electric and magnetic fields.

B is wrong as an answer: it is a true property; uncharged X-rays are not deflected by magnetic fields.

C is wrong as an answer: high penetrating power is exactly what makes X-rays useful in medicine and security checks.

D is wrong as an answer: their wavelength is indeed far smaller than that of visible light.

Exam tip: X-rays and gamma rays are uncharged, so no deflection in fields; alpha and beta particles are charged and do get deflected.

The correct answer is A, Disaster Reduction. The United Nations Sasakawa Award for Disaster Risk Reduction honours people and institutions that work to reduce the risk of disasters.

The award was set up in 1986 with a gift from Ryoichi Sasakawa, founder of the Japanese philanthropic body now known as the Nippon Foundation. It is managed by the United Nations Office for Disaster Risk Reduction (UNDRR) and is presented in alternate years at the Global Platform for Disaster Risk Reduction. India's Pradeep Kumar Mishra, then Additional Principal Secretary to the Prime Minister, received it in 2019 for his work on disaster management, which is why it appeared in exams that year.

B is wrong: UN peacekeepers are honoured by the Dag Hammarskjöld Medal, not the Sasakawa Award.

C is wrong: health work is recognised by a separate WHO prize; the UN Sasakawa Award is for disaster risk reduction.

D is wrong: the award is not given for poverty alleviation.

Exam tip: UN Sasakawa Award = disaster risk reduction, run by UNDRR; P. K. Mishra won it in 2019.

The correct answer is B, Achieving the target of net zero emissions by 2047. India's net zero target announced at COP-26 is the year 2070, not 2047.

At COP-26 in Glasgow in November 2021, Prime Minister Narendra Modi announced five commitments called the Panchamrit (five nectar elements). They are: 500 GW of non-fossil fuel energy capacity by 2030; meeting 50 percent of energy requirements from renewable energy by 2030; cutting total projected carbon emissions by one billion tonnes by 2030; reducing the carbon intensity of the economy by 45 percent over 2005 levels by 2030; and reaching net zero emissions by 2070. The year 2047 is the target of Viksit Bharat, the centenary of independence, which is why it is used as a distractor.

A is wrong: 50 percent of energy needs from renewables by 2030 is one of the five elements.

C is wrong: the 45 percent cut in carbon intensity over 2005 levels is part of the Panchamrit.

D is wrong: the one billion tonne cut in projected emissions is also part of it.

Exam tip: Panchamrit = 500 GW, 50 percent, 1 billion tonnes, 45 percent, net zero by 2070.

The correct answer is C, The number of protons is same as atomic number. The atomic number (Z) is defined as the number of protons in the nucleus of an atom.

Every atom of an element has the same number of protons, so the atomic number identifies the element: hydrogen has 1, carbon 6 and oxygen 8. In a neutral atom the number of electrons equals the number of protons, which is why electrons are often counted to find Z. The modern periodic table, based on Moseley's work of 1913, arranges elements in order of increasing atomic number.

A is wrong: the number of neutrons can differ among atoms of the same element; such atoms are isotopes.

B is wrong: electrons plus neutrons is not a defined quantity in atomic structure.

D is wrong: protons plus neutrons gives the mass number (A), not the atomic number.

Exam tip: atomic number Z = protons; mass number A = protons + neutrons; neutrons = A minus Z.

The correct answer is B, Visit the town incognito. Kautilya's daily time-table for the king does not include moving through the town in disguise; he learns about his people through spies instead.

The Arthashastra, attributed to Kautilya (Chanakya), the minister of Chandragupta Maurya, divides the king's day and night into eight parts each. In the first part of the day the king hears reports on defence and on receipts and expenditure; later he looks into the affairs of citizens, receives revenue in cash and appoints heads of departments, corresponds with his council of ministers and receives secret reports, and reviews his army and plans campaigns with his commander. Gathering news is left to an elaborate network of spies, not to the king's own secret visits.

A is wrong: hearing reports on defence comes in the first part of the day.

C is wrong: receiving revenue in cash is a set duty of the fourth part of the day.

D is wrong: consulting the council of ministers is part of the schedule.

Exam tip: Arthashastra = Kautilya, 15 books (adhikaranas); the king's day and night each have eight parts.

The correct answer is B, Formed calcium sulphate is insoluble in water and covers the calcium metal, preventing it from reacting any further. The product forms a coating that shuts the acid out.

Calcium reacts with dilute sulphuric acid to give calcium sulphate and hydrogen gas: Ca + H2SO4 gives CaSO4 + H2. Calcium sulphate dissolves only very slightly in water, so it does not wash away; it settles as a layer on the surface of the metal. Once the metal is covered, fresh acid cannot reach it and the fizzing soon stops. The same thing happens when lead is put in dilute sulphuric acid, because lead sulphate is also insoluble.

A is wrong: the reaction starts readily at room temperature, which is why hydrogen is seen at once.

C is wrong: gypsum (CaSO4.2H2O) does contain two water molecules, but this does not explain why the reaction stops.

D is wrong: calcium sulphate is a stable compound.

Exam tip: an insoluble sulphate coat (calcium, lead) stops a metal's reaction with sulphuric acid.

The correct answer is A, linear momentum. The de Broglie wavelength depends only on momentum, so equal wavelengths mean equal momenta.

In 1924 Louis de Broglie proposed that every moving particle has a wave linked to it, with wavelength λ = h/p, where h is Planck's constant and p is the linear momentum. For a photon the same relation holds, p = h/λ. So if an electron and a photon have the same wavelength, their momenta must be the same. Their other quantities still differ: the photon's energy is pc, while the electron's kinetic energy is p²/2m, which is much smaller for the same momentum. De Broglie's idea was confirmed by the Davisson-Germer electron diffraction experiment of 1927.

B is wrong: for the same momentum a photon carries far more energy than the electron.

C is wrong: the photon always moves at the speed of light, the electron much more slowly.

D is wrong: angular momentum does not enter the de Broglie relation.

Exam tip: λ = h/p; same wavelength = same momentum, not the same energy or speed.

The correct answer is C, 14%. The real interest rate is the nominal rate minus the rate of inflation: 24 minus 10 gives 14 percent.

The nominal interest rate is the rate written on the loan, here 24 percent a year. Inflation reduces the buying power of the money repaid, so the true cost of borrowing, or the true return to the lender, is lower. Economists measure it with the Fisher relation, real rate ≈ nominal rate − inflation rate. When inflation is higher than the nominal rate, the real rate becomes negative, which favours borrowers over savers. Central banks such as the RBI watch real rates when they set the repo rate.

A is wrong: 240 percent comes from multiplying the two rates, which has no economic meaning.

B is wrong: 34 percent adds inflation to the nominal rate instead of subtracting it.

D is wrong: 4 percent does not follow from any correct use of the two figures.

Exam tip: real interest rate = nominal rate − inflation (Fisher effect); higher inflation helps borrowers.

The correct answer is B, 1, 3 and 4. Springs appear where groundwater meets a barrier or a surface outlet, which happens in jointed rocks, karst areas and tilted strata, but not commonly in dry regions.

A spring is a natural outflow of groundwater at the surface. In well-jointed rocks such as granite, water moves down the joints and comes out where a joint meets a valley side. In karst (limestone) country, water dissolves channels and caves underground and emerges as large springs at the base of the limestone. In tilted strata, water sinks into a permeable layer lying over an impermeable one and flows out where that boundary reaches the surface, often along a hill slope or escarpment.

A is wrong: it leaves out tilted strata, which are a classic site for springs.

C is wrong: arid areas have too little rainfall to feed many springs, and it misses jointed rocks and karst.

D is wrong: it leaves out well-jointed rocks.

Exam tip: springs need water in, a path down and an exit: joints, karst channels and permeable over impermeable beds.

The correct answer is B, Indra Sawhney vs. Union of India. In this 1992 case, also called the Mandal case, the Supreme Court held that the creamy layer must be kept out of OBC reservation.

A nine-judge bench upheld 27 percent reservation for Other Backward Classes in central government jobs, as recommended by the Mandal Commission. It ruled that the better-off section of the backward classes, the creamy layer, should not get the benefit, set a ceiling of 50 percent on total reservation in normal circumstances, and held that there should be no reservation in promotions (a point later changed by the 77th Amendment). The government then set income and status limits to identify the creamy layer.

A is wrong: the Nanavati case of 1961 was a murder trial, famous for ending jury trials in India.

C is wrong: Madhu Limaye vs. Ved Murti was a contempt-of-court matter.

D is wrong: Sajjan Singh (1965) dealt with Parliament's power to amend fundamental rights.

Exam tip: Indra Sawhney (1992) = Mandal case: 27 percent OBC quota, creamy layer out, 50 percent cap.

The correct answer is C, Photosynthesis. Photosynthesis absorbs energy from sunlight to build glucose, so it is an endothermic process.

An endothermic process takes in heat or light from its surroundings, while an exothermic one gives energy out. In photosynthesis, green plants use light energy trapped by chlorophyll to combine carbon dioxide and water into glucose and oxygen: 6CO2 + 6H2O + light energy gives C6H12O6 + 6O2. The energy is stored in the chemical bonds of glucose. Other common endothermic changes are melting ice, evaporating water and decomposing calcium carbonate by heat.

A is wrong: burning carbon gives out heat; it is exothermic.

B is wrong: neutralisation of an acid by an alkali releases heat, so the mixture warms up.

D is wrong: respiration breaks down glucose and releases energy; it is exothermic and is the reverse of photosynthesis.

Exam tip: photosynthesis stores energy (endothermic); respiration, combustion and neutralisation release it (exothermic).

The correct answer is B, Mitochondria. Mitochondria carry their own circular DNA and their own ribosomes, so they can make some of their own proteins.

Mitochondria are the sites of aerobic respiration, where ATP is produced, which is why they are called the powerhouse of the cell. They have a double membrane, the inner one folded into cristae. Their DNA is circular like that of bacteria and their ribosomes are of the smaller 70S type, which supports the endosymbiotic theory that they began as free-living bacteria taken in by an early cell. Chloroplasts in plant cells are the other organelle with their own DNA and ribosomes, and mitochondrial DNA is inherited from the mother.

A is wrong: the Golgi apparatus packages and sends out proteins but has no DNA of its own.

C is wrong: lysosomes hold digestive enzymes and have no DNA.

D is wrong: nucleosomes are not organelles; they are units of DNA wound round histone proteins inside the nucleus.

Exam tip: semi-autonomous organelles = mitochondria and chloroplasts (own DNA, 70S ribosomes).

The correct answer is B, Violet. Violet light has the shortest wavelength among the visible colours, so the medium bends it the most.

The splitting of white light into its colours is called dispersion. It happens because the refractive index of a medium such as glass or water is slightly different for each wavelength: it is highest for violet and lowest for red. A higher refractive index means more bending, so violet is deviated the most and red the least. The colours come out in the order VIBGYOR, with red at the top and violet at the bottom of the spectrum. Newton first showed this with a glass prism, and a rainbow is the same effect in raindrops.

A is wrong: red has the longest wavelength and is deviated the least.

C is wrong: green lies in the middle of the spectrum, so its deviation is in between.

D is wrong: if every colour bent equally, white light would not split at all.

Exam tip: shorter wavelength, greater refractive index, greater deviation: violet most, red least.

The correct answer is D, surface tension. Where oil meets water, the unequal pull of their molecules sets up a surface (interfacial) tension that keeps the two liquids as separate layers.

Water molecules are polar and hold one another strongly through hydrogen bonds, while oil molecules are non-polar and attract water only weakly. Each liquid's molecules prefer their own kind, so the boundary between them behaves like a stretched skin that tries to shrink to the smallest area. That is why oil shaken with water breaks into drops and then gathers again into a layer, floating on top because it is less dense. Soaps and detergents lower this tension, which lets oil spread into water as an emulsion and wash away.

A is wrong: bulk modulus measures how hard a substance is to compress, not whether two liquids mix.

B is wrong: shear strain is the change of shape of a body under a sideways force.

C is wrong: 'volume effect' is not the physical property that decides mixing.

Exam tip: like dissolves like; detergents cut the oil-water surface tension and make emulsions.

The correct answer is A, Methanol. Methanol (CH3OH) is called wood spirit or wood alcohol because it was first obtained by the destructive distillation of wood.

Methanol is the simplest alcohol. When wood is heated strongly without air, it gives off vapours from which methanol was separated, hence the old name. Today it is made mostly from synthesis gas (carbon monoxide and hydrogen). Methanol is highly poisonous: even small amounts can cause blindness or death, and it is added to industrial ethanol to make denatured spirit that cannot be drunk. It is used as a solvent, an antifreeze and a fuel.

B is wrong: ethanol (C2H5OH) is grain alcohol or spirit of wine, made by fermenting sugars.

C is wrong: formaldehyde (methanal) is a gas whose 40 percent solution in water is formalin, used to preserve specimens.

D is wrong: acetaldehyde (ethanal) is formed when ethanol is oxidised; it is not called wood spirit.

Exam tip: wood spirit = methanol (poisonous); grain alcohol = ethanol; formalin = formaldehyde solution.

The correct answer is B, Jawaharlal Nehru and Sardar Patel represented Congress to negotiate with the mission. Congress was represented by Jawaharlal Nehru and Maulana Abul Kalam Azad, its president, not by Sardar Patel.

With Japan advancing in South-East Asia, the British War Cabinet sent Sir Stafford Cripps to India in March 1942, after he had persuaded it to accept a draft declaration. It promised dominion status after the war, a constitution-making body elected by the provincial assemblies with members from the princely states, and the right of any province to stay out of the new union. Congress rejected it because defence would stay in British hands now and the provincial option threatened partition; Gandhi called it a post-dated cheque.

A is wrong: the War Cabinet did approve Cripps's draft declaration in March 1942.

C is wrong: dominion status after the war was the main offer.

D is wrong: a constitution-making body after the war was also offered.

Exam tip: Cripps Mission 1942: Congress side Nehru and Azad; 'post-dated cheque'; failure led to Quit India.

The correct answer is D, Cerium oxide. Cerium oxide (CeO2) strongly absorbs ultraviolet rays while letting visible light through, so it is added to glass to make it UV-protective.

Cerium is a rare earth element, one of the lanthanides. Its oxide absorbs UV radiation and stops the glass from darkening (solarising) under strong sunlight or radiation, which is why it is used in sunglasses, spectacle lenses, glass for vehicles and buildings, and glass that shields electronic parts. Cerium oxide is also the standard powder for polishing glass and lenses, and it serves as a catalyst in vehicle exhaust converters.

A is wrong: aluminium oxide (alumina) is used as an abrasive and in hard ceramics, not as a UV absorber in glass.

B is wrong: tungsten oxide is known for its use in electrochromic smart windows that change colour with voltage.

C is wrong: molybdenum oxide is used mainly as a catalyst and in alloys, not for UV-protective glass.

Exam tip: cerium oxide = UV-absorbing glass and glass polishing; cerium is a lanthanide (rare earth).

The correct answer is D, tRNA. Transfer RNA picks up a specific amino acid and brings it to the ribosome, where it is added to the growing protein chain.

Each tRNA molecule is folded into a clover-leaf shape. One end carries an amino acid, attached by an enzyme that matches each tRNA to its own amino acid, and the anticodon loop at the other end has three bases that pair with a codon on the messenger RNA. In this way tRNA acts as the adapter that reads the genetic code and delivers the right amino acid in the right order during translation. The idea of such an adapter molecule was first proposed by Francis Crick.

A is wrong: mRNA carries the coded message from DNA to the ribosome but does not carry amino acids.

B is wrong: snRNA (small nuclear RNA) helps in splicing, the removal of introns from pre-mRNA.

C is wrong: miRNA (micro RNA) regulates genes by silencing particular mRNAs.

Exam tip: mRNA = message (codons); tRNA = adapter carrying amino acids (anticodon); rRNA = part of the ribosome.

The correct answer is D, 1, 2 and 3. The triple point is the single temperature and pressure at which the solid, liquid and vapour phases of a substance exist together in equilibrium.

On a phase diagram, the lines dividing solid from liquid, liquid from vapour and solid from vapour meet at one point, the triple point. For water it lies at 273.16 K (0.01 °C) and a pressure of about 611.66 pascals, far below normal air pressure. Because it is fixed and easy to reproduce, the triple point of water was long used to define the kelvin. At pressures below the triple point a solid turns straight into vapour, which is sublimation; dry ice does this at ordinary pressure.

A is wrong: the liquid phase alone describes ordinary conditions, not the triple point.

B is wrong: solid and liquid together is the melting point, where vapour is not needed.

C is wrong: solid and vapour together is the sublimation curve, below the triple point.

Exam tip: triple point = all three phases; water's is 0.01 °C (273.16 K) at about 611.66 Pa.

The correct answer is D, Banaras and the Surrounding tracts were detached from Awadh and handed over to Shah Alam II. The districts taken from Awadh and given to Shah Alam II were Kora and Allahabad, not Banaras.

After the Battle of Buxar (1764), Robert Clive signed two treaties at Allahabad in August 1765. By the first, the Mughal Emperor Shah Alam II issued a farman granting the Company the Diwani, the right to collect revenue, of Bengal, Bihar and Orissa, in return for an annual payment of 26 lakh rupees; he also received Kora and Allahabad. By the second, Nawab Shuja-ud-Daula got Awadh back on paying 50 lakh rupees as war indemnity, and Balwant Singh, the zamindar of Banaras, kept his estates.

A is wrong: the treaty was indeed signed in 1765.

B is wrong: the grant of the Diwani by the emperor's farman is the treaty's best-known term.

C is wrong: Awadh was restored to Shuja-ud-Daula for 50 lakh rupees.

Exam tip: Treaty of Allahabad 1765: Diwani to the Company; Kora and Allahabad to Shah Alam II; 50 lakh from Awadh.