Current Affairs 29 September 2026: Today's GK & MCQs

The correct answer is B, Cones. Cones are the photoreceptor cells of the retina that respond to colour in bright light. The human retina carries two kinds of photoreceptors. Cones number about six to seven million, sit densely near the centre of the retina and come in three types, sensitive to red, green and blue light; the brain mixes their signals into every shade we see. They work only when the light is good, which is why colours fade at dusk. Option A is wrong because rods are far more numerous but work in dim light and give only shades of grey, not colour. Option C is wrong because the blind spot is the point where the optic nerve leaves the eyeball and carries no photoreceptors at all. Option D is wrong because the fovea is a small pit in the retina, a place rather than a cell type, although it is packed with cones. Exam tip: rods for night and grey, cones for colour and daylight; colour blindness is a defect of the cones.

The correct answer is A, the air pressure is less. A liquid boils when its vapour pressure equals the pressure of the air pressing on its surface, so lower air pressure means a lower boiling point. At sea level the atmosphere presses with about 101 kilopascals and water boils at 100 degrees Celsius. On a hill station the column of air above is shorter, the pressure falls, and water may boil at 90 degrees or less, which is why rice and pulses cook slowly in the mountains and a pressure cooker, which raises the pressure inside, is used to cook them faster. Option B is wrong because the surrounding temperature only decides how long heating takes, not the temperature at which boiling begins. Option C is wrong because the latent heat of vaporisation is a property of water and does not shrink with altitude. Option D is wrong because option A already states the correct reason. Exam tip: boiling point rises with pressure and falls with altitude; that single rule explains both the cooker and the hill station.

The correct answer is A, Bryophytes. Bryophytes live on land but still need water to complete reproduction, so they are called the amphibians of the plant kingdom. Mosses, liverworts and hornworts belong here. They grow in damp, shady places, have no true roots, stems or leaves and no vascular tissue, so water moves through them by simple absorption. Their male gametes swim to the egg through a film of water, which ties them to moist ground exactly as frogs are tied to ponds. Option B is wrong because thallophytes are the algae, mostly water plants that never left water. Option C is wrong because pteridophytes, the ferns, are the first plants with true vascular tissue, xylem and phloem. Option D is wrong because gymnosperms such as pine and cycas bear naked seeds and use pollen, not swimming gametes. Exam tip: bryophytes are amphibians of the plant kingdom, pteridophytes are the first vascular plants, and gymnosperms are the first seed plants.

The correct answer is A, James Chadwick. Chadwick discovered the neutron in 1932 and won the Nobel Prize in Physics for it in 1935. He bombarded beryllium with alpha particles and found that the radiation given off was not affected by electric or magnetic fields, yet could knock protons out of paraffin. The only explanation was a particle with no charge and a mass close to that of the proton, which he named the neutron. It completed the picture of the atom, since the nucleus had earlier been short of mass, and it later made nuclear fission possible. Option B is wrong because Rutherford discovered the nucleus through his gold foil experiment and is credited with the proton. Option C is wrong because J. J. Thomson discovered the electron in 1897 with his cathode ray tube. Option D is wrong because John Dalton gave the atomic theory in 1803, long before subatomic particles were known. Exam tip: Thomson for the electron, Rutherford for the proton and nucleus, Chadwick for the neutron.

The correct answer is A, Asia. Asia takes the largest share of India’s exports, close to half of the total, far ahead of any other continent. The reason is geography and trade policy together: India’s biggest regional markets are its own neighbourhood and West Asia, where the United Arab Emirates, Singapore, Bangladesh, China and Saudi Arabia buy petroleum products, engineering goods, gems and jewellery, rice and pharmaceuticals. Short shipping routes, free trade agreements with ASEAN and a large Indian diaspora in the Gulf all add to the flow. Option B is wrong because Europe is the second largest destination region but well behind Asia. Option C is wrong because Africa, though a growing market for Indian medicines and vehicles, takes only a small share. Option D is wrong because North America is dominated by the United States, which is India’s largest single export partner, yet one country cannot outweigh a whole continent. Exam tip: by continent it is Asia, by country the United States; the two facts are asked in exactly this way.

The correct answer is A, strength of the intermolecular forces of attraction. Melting means breaking the particles free of the forces holding them in a fixed lattice, so a higher melting point means stronger forces of attraction. Heat supplied at the melting point does not raise the temperature at all; it is used as latent heat of fusion to overcome those attractions. This is why ionic solids such as common salt melt near 800 degrees Celsius while wax, held together by weak forces, melts in the warmth of a hand. Option B is wrong because repulsive forces act only when particles are pushed very close and they do not hold a solid together. Option C is wrong because molecular mass is a poor guide, as heavy iodine melts far below lighter silica. Option D is wrong because size matters only through the strength of the forces it creates, not on its own. Exam tip: stronger intermolecular forces mean a higher melting point and a higher boiling point together.

The correct answer is A, Sodium bicarbonate (Sodium hydrogen carbonate). Baking soda is sodium hydrogen carbonate, NaHCO3, a mild base made by the Solvay process from brine, ammonia and carbon dioxide. On heating, or on meeting an acid such as the tartaric acid in baking powder, it gives off carbon dioxide, and it is these bubbles that make bread and cake rise. The same reaction makes it useful in soda acid fire extinguishers and as an antacid, since it neutralises excess hydrochloric acid in the stomach. Option B is wrong because sodium carbonate, Na2CO3, is washing soda, a much stronger base used for cleaning and in glass making. Option C is wrong because potassium bicarbonate is a different salt, used in some fire extinguishers and fertilisers, not in the kitchen. Option D is wrong because potassium carbonate is potash, used in soap and glass. Exam tip: baking soda NaHCO3, washing soda Na2CO3.10H2O, caustic soda NaOH, and bleaching powder Ca(OCl)Cl.

The correct answer is D, V D Savarkar. Vinayak Damodar Savarkar founded Abhinav Bharat at Nashik in 1904, together with his brother Ganesh. It grew out of an earlier group called Mitra Mela and took its name from Mazzini’s Young Italy, whose biography Savarkar translated into Marathi. The society trained young men in arms, spread revolutionary literature and had branches in Maharashtra and later in London, where Savarkar went on a scholarship and wrote The Indian War of Independence 1857. It was finally disbanded in 1952. Option A is wrong because Khudiram Bose was a young Anushilan Samiti revolutionary hanged in 1908 for the Muzaffarpur bomb case. Option B is wrong because Shyamji Krishna Verma founded the India House and the Indian Home Rule Society in London in 1905. Option C is wrong because Lala Har Dayal led the Ghadar Party, started in San Francisco in 1913. Exam tip: Abhinav Bharat 1904 Savarkar, India House 1905 Shyamji Krishna Verma, Ghadar Party 1913 Har Dayal.

The correct answer is A, it proposed that the Indian magistrates would try Europeans in criminal cases. The Ilbert Bill of 1883 sought to remove the rule that European British subjects could be tried only by European judges. It was drafted by Sir Courtenay Ilbert, the law member of Lord Ripon’s council, and would have let Indian district magistrates and sessions judges hear criminal cases against Europeans. The European community in India protested so fiercely that the bill was watered down in 1884, giving a European the right to be tried by a jury half of whose members were European. The episode taught educated Indians the value of organisation and is counted among the immediate causes of the founding of the Indian National Congress in 1885. Option B is wrong because Indians could already file such cases. Option C is wrong because the bill spoke of Indian judges and magistrates generally, not of ICS officers alone. Option D is wrong because Ilbert wrote the bill; the agitation was against it. Exam tip: Ilbert Bill 1883, Lord Ripon, and the Congress in 1885.

The correct answer is B, Cytoplasm. Bacteria are prokaryotes, so their DNA lies free in the cytoplasm instead of being packed inside a nucleus. The single circular chromosome sits in a region of the cytoplasm called the nucleoid, which has no nuclear membrane around it. Many bacteria also carry small extra rings of DNA called plasmids, which often hold genes for antibiotic resistance and are the tools used to move genes in biotechnology. Option A is wrong because a true nucleus with a membrane is found only in eukaryotes such as plants, animals and fungi; bacteria have no such organelle. Option C is wrong because the cell membrane only controls what enters and leaves the cell, although the chromosome is loosely attached to it at one point. Option D is wrong because ribosomes, of the smaller 70S type in bacteria, build proteins from the instructions in the DNA and store no genetic material themselves. Exam tip: prokaryotes have a nucleoid and 70S ribosomes; eukaryotes have a true nucleus and 80S ribosomes.

The correct answer is C, because the Suez Canal has no locks at all. It is a sea level canal: the Mediterranean and the Red Sea stand at almost the same height, so ships sail straight through without being raised or lowered. The canal, about 193 km long, was built under Ferdinand de Lesseps and opened in November 1869 across the Isthmus of Suez in Egypt, separating Africa from Asia. Egypt nationalised it in 1956. Options A, B and D all state facts, so none of them is the answer: the canal did open in 1869, it does join the Mediterranean to the Red Sea through the Gulf of Suez, and it did shorten the voyage from Europe to India by thousands of kilometres, ending the long route round the Cape of Good Hope. Exam tip: Suez is a lock free canal; the Panama Canal is the one with locks, because Gatun Lake lies well above sea level.

The correct answer is C, a mechanism to reduce CO2 emission. A nuclear reactor splits heavy atoms; it burns no fuel, so it releases no carbon dioxide and needs no equipment to cut such emissions. The heat of fission is produced in the reactor core, carried away by a coolant, passed to water in a heat exchanger or steam generator, and the steam then turns a turbine coupled to a generator. Control rods of cadmium or boron absorb spare neutrons and a moderator such as heavy water slows them down so that fission continues steadily. Option A is wrong as a choice because the turbine is the part that actually converts steam energy into electricity. Option B is wrong because the heat exchanger carries heat from the radioactive coolant loop to the clean water loop. Option D is wrong because the reaction chamber, the core holding the fuel rods, is where fission happens. Exam tip: a nuclear plant emits no carbon dioxide; its waste problem is spent radioactive fuel instead.

The correct answer is D, Polarization. Only a transverse wave can be polarised, so the polarisation of light proves that its vibrations are at right angles to the direction of travel. In ordinary light the electric field vibrates in every plane around the ray. A polaroid sheet lets through only the vibrations in one plane, and a second polaroid turned at ninety degrees then blocks the light completely. A longitudinal wave such as sound, whose particles vibrate along the direction of travel, has no such plane and can never be polarised. Sunglasses, camera filters and LCD screens all use this property. Option A is wrong because refraction, the bending of light on entering a denser medium, happens with sound waves too. Option B is wrong because diffraction, the spreading of a wave at an edge, is shown by all waves. Option C is wrong because interference only proves that light is a wave, not which kind. Exam tip: interference and diffraction prove light is a wave; polarisation proves it is a transverse wave.

The correct answer is D, 8(1). Section 8(1) of the Indian Independence Act, 1947 gave the Constituent Assembly of each new Dominion the powers of its legislature. The Act was passed by the British Parliament on 18 July 1947 and came into force on 15 August 1947. It divided British India into the two Dominions of India and Pakistan, ended British paramountcy over the princely states, and allowed the Constituent Assembly of each Dominion to work both as its ordinary law-making body and as the body framing its Constitution. India's Assembly, elected in 1946 under the Cabinet Mission Plan, therefore became a sovereign body from 15 August 1947 and no longer needed British approval for its work. Option A is wrong because Section 6 deals with the law-making powers of the new Dominion legislatures. Option B is wrong because Section 10 continues the service conditions of officers of the Secretary of State's services. Option C is wrong because Section 12 deals with British forces stationed in India. Exam tip: Indian Independence Act 1947, Section 8 is the Constituent Assembly clause; the Act came into force on 15 August 1947.

The correct answer is A, Loo. The Loo is the hot, dry, dusty wind that blows over the plains of north India in summer. It develops in May and June, usually from the west or north-west, and blows strongest in the afternoon, when temperatures can cross 45 degrees Celsius in Rajasthan, Punjab, Haryana, Delhi and Uttar Pradesh. Long exposure to it causes heat stroke, so schools and outdoor work stop in the afternoon during a Loo spell. It weakens once the monsoon reaches the plains. Option B is wrong because the Chinook is a warm, dry wind that descends the eastern slopes of the Rocky Mountains in North America and is nicknamed the snow-eater. Option C is wrong because mango showers are pre-monsoon rain in Kerala, Karnataka and Tamil Nadu that helps mangoes ripen, not a wind. Option D is wrong because Purga is a cold, snow-laden wind of the Siberian tundra. Exam tip: Loo is hot and Indian, Chinook is American and warm, Purga is Siberian and cold.

The correct answer is D, Ricky Kej. Ricky Kej won the Grammy for Best New Age Album at the 57th Grammy Awards in 2015 for Winds of Samsara, made with the South African flautist Wouter Kellerman. The album drew on the lives of Mahatma Gandhi and Nelson Mandela and reached the top of the Billboard New Age chart in the United States, the first Indian album to do so. Kej is a Bengaluru-based composer who works on environmental themes and is a UNICEF and UNESCO goodwill figure; he won a second Grammy in 2022 for Divine Tides, made with Stewart Copeland of The Police. Option A is wrong because Mano Murthy composes for Kannada cinema and has not won a Grammy. Option B is wrong because Raghu Dixit is a Bengaluru folk-rock singer with no Grammy. Option C is wrong because Subhashish Ghosh has no link with this album. Exam tip: Winds of Samsara means Ricky Kej with Wouter Kellerman, Grammy 2015; Divine Tides means Ricky Kej with Stewart Copeland.

The correct answer is B, Kerala. Kolathunadu, Valluvanad and Thekkumkoor were small medieval kingdoms, or swaroopams, of Kerala. Kolathunadu, ruled by the Kolathiri rajas, lay in north Malabar around present-day Kannur; Valluvanad spread over the Palakkad and Malappuram area and is remembered for the Mamankam festival at Tirunavaya; Thekkumkoor lay in the Kottayam region and was absorbed by Travancore under Marthanda Varma in the eighteenth century. Before unification, Kerala was split among such chiefdoms along with Travancore, Cochin and Calicut, and the present state was formed on 1 November 1956 from Travancore-Cochin and the Malabar district of Madras. Option A is wrong because Karnataka's old kingdoms were the Kadambas, Hoysalas and Vijayanagara. Option C is wrong because ancient Bihar was home to Magadha, Anga and Videha. Option D is wrong because Gujarat was ruled by the Solankis of Anhilwada and the Chaulukyas. Exam tip: names ending in nadu or koor in this list point to the medieval chiefdoms of Kerala.

The correct answer is D, Santhal Revolt. The Santhal rebellion, called the Hool, was led by the brothers Sidhu and Kanhu Murmu. It broke out in 1855 in the Rajmahal hills of the Damin-i-Koh tract, in what is now Jharkhand, when Santhal peasants rose against moneylenders, zamindars, contractors and the police who had taken their land and pushed them into bonded debt. Thousands gathered at Bhagnadih, declared their own rule and marched on the plains; the British put the rising down by 1856 after heavy fighting, and Sidhu and Kanhu were killed. The government then created the separate Santhal Parganas district with special protective rules. Option A is wrong because the Bhil risings of Khandesh were led by Sewaram and later Govind Guru. Option B is wrong because the Khasi revolt in the Meghalaya hills was led by Tirot Sing. Option C is wrong because the Munda rebellion, the Ulgulan of 1899, was led by Birsa Munda. Exam tip: Hool 1855 means Sidhu and Kanhu; Ulgulan 1899 means Birsa Munda.

The correct answer is B, Mughals. After Guru Gobind Singh died at Nanded in 1708, Banda Singh Bahadur led the Sikhs in revolt against Mughal rule in Punjab. He gathered peasants of the Malwa and Doaba tracts, sacked Samana and Sadhaura, and in 1710 won his best-known victory at Sirhind, where the governor Wazir Khan, held responsible for the killing of the Guru's young sons, was defeated and slain. Banda set up his base at Lohgarh, struck coins and issued orders in the name of the Gurus, and ended the zamindari system in the tracts he held by giving land to those who tilled it. He was besieged at Gurdaspur, captured in 1715 and put to death at Delhi in 1716 in the reign of Farrukhsiyar. Option A is wrong because the Gurkhas ruled Nepal and fought the British in 1814-16. Option C is wrong because British power reached Punjab only in 1849. Option D is wrong because the Marathas were never his target. Exam tip: 1708 Guru Gobind Singh, 1710 Sirhind, 1716 Banda's execution.

The correct answer is C, 1 and 2 only. Statement 3 is wrong because the Kaleshwaram project is built on the Godavari, not the Krishna. The scheme takes its name from Kaleshwaram in Telangana, near the point where the Pranhita joins the Godavari, and it was inaugurated in June 2019, which makes statement 1 correct. It is described as the world's largest multi-stage, multi-purpose lift irrigation project, so statement 2 is correct: water is raised through a long chain of pump houses, barrages, tunnels, canals and reservoirs to fields that lie far above the river, and it is meant to serve lakhs of hectares in north Telangana as well as drinking water and industry. Option A is wrong and option D is wrong because both accept statement 3 and its Krishna River claim. Option B is wrong because it leaves out the correct statement 2. Exam tip: Kaleshwaram is on the Godavari in Telangana, while Polavaram is on the Godavari in Andhra Pradesh.

The correct answer is A, Khetri. Khetri, in the Jhunjhunu district of Rajasthan, is famous for its copper mines. The Khetri belt runs along the Aravalli range, and its ore is mined and processed by Hindustan Copper Limited, which set up the Khetri Copper Complex there. Rajasthan is the country's leading copper state, followed by Madhya Pradesh with the Malanjkhand mine in Balaghat and Jharkhand with the Singhbhum belt. Copper is valued because it conducts electricity and heat well and is ductile, so it goes into wires, cables, utensils and alloys such as brass and bronze. Option B is wrong because Keonjhar in Odisha is known for iron ore and manganese. Option C is wrong because Gaya in Bihar lies in the mica belt and has no copper mining. Option D is wrong because Satna in Madhya Pradesh is known for limestone and its cement plants. Exam tip: for copper remember Khetri in Rajasthan, Malanjkhand in Madhya Pradesh and Singhbhum in Jharkhand.

The correct answer is C, Debendranath Tagore. Debendranath Tagore founded the Tattvabodhini Sabha in Calcutta in 1839 to study the Upanishads and Vedanta and to spread the rational religion that Rammohun Roy had preached. The Sabha ran a school and brought out the Tattvabodhini Patrika, a journal that carried writings on religion, science and social reform; Iswar Chandra Vidyasagar and Akshay Kumar Datta were among its members. Debendranath, the father of Rabindranath Tagore, joined the Brahmo Sabha in 1843 and reorganised it as the Brahmo Samaj, and the Tattvabodhini Sabha merged into it in 1859. Option A is wrong because Keshab Chandra Sen joined the Brahmo Samaj much later and broke away to form the Brahmo Samaj of India in 1866. Option B is wrong because Rammohun Roy founded the Brahmo Sabha in 1828 and died in 1833, before this body was set up. Option D is wrong because Dayanand Saraswati founded the Arya Samaj in 1875 at Bombay. Exam tip: Brahmo Sabha 1828 Rammohun Roy, Tattvabodhini Sabha 1839 Debendranath Tagore, Arya Samaj 1875 Dayanand Saraswati.

The correct answer is C, 1 - C, 2 - A, 3 - D, 4 - B. BALCO, the Bharat Aluminium Company, has its smelter at Korba in Chhattisgarh, where cheap thermal power and nearby bauxite made aluminium smelting possible. IISCO, the Indian Iron and Steel Company, works at Burnpur near Asansol in West Bengal, in the Damodar valley coal and iron belt. NFL, National Fertilizers Limited, runs its gas-based urea plant at Bhatinda in Punjab, close to the farm belt it supplies. ICF, the Integral Coach Factory, is at Perambur in Chennai, Tamil Nadu, and has been building railway coaches since 1955. Option A is wrong because it pairs BALCO with Burnpur and IISCO with Chennai. Option B is wrong because it sends NFL to Chennai and ICF to Bhatinda. Option D is wrong because it places BALCO at Bhatinda and ICF at Korba. Exam tip: aluminium goes with Korba, steel with Burnpur, fertiliser with Bhatinda and coaches with Chennai.

The correct answer is A, Satyendra Prasanna Sinha. The 1915 session of the Indian National Congress, held at Bombay, was presided over by Satyendra Prasanna Sinha, later Lord Sinha of Raipur. He was the first Indian appointed to the Governor-General's Executive Council, in 1909, and went on to become Under-Secretary of State for India and Governor of Bihar and Orissa, the first Indian to govern a province. His presidency came in the year Gopal Krishna Gokhale and Pherozeshah Mehta died and Gandhi returned from South Africa, so the session marks a turning point for the party. Option B is wrong because Ambica Charan Mazumdar presided at Lucknow in 1916, where the Congress and the Muslim League signed their pact and the moderates and extremists reunited. Option C is wrong because Bhupendra Nath Bose presided at Madras in 1914. Option D is wrong because Madan Mohan Malaviya presided at Lahore in 1909 and at the Delhi special session in 1918. Exam tip: 1914 Madras Bose, 1915 Bombay Sinha, 1916 Lucknow Mazumdar.

The correct answer is C, Jahangir. Mughal painting reached its peak under Jahangir, who ruled from 1605 to 1627. He was a keen collector who claimed he could name the artist behind every figure in a painting, and his studio turned from long illustrated histories to single studies of portraits, birds, animals, flowers and court scenes, with fine European touches such as shading and the halo. Ustad Mansur, titled Nadir-ul-Asr for his birds and animals, Abul Hasan, titled Nadir-uz-Zaman, Bishandas for portraits and Manohar all worked for him. Option A is wrong because Humayun only brought the Persian masters Mir Sayyid Ali and Abdus Samad to India, and little painting survives from his unsettled reign. Option B is wrong because Akbar founded and built up the school with works such as the Razmnama and the Akbarnama, but its finest phase came later. Option D is wrong because under Shah Jahan painting grew formal and cold as he turned to architecture. Exam tip: Akbar founded, Jahangir perfected, Shah Jahan formalised and Aurangzeb withdrew support from Mughal painting.

The correct answer is C, single-member body. Article 148 of the Constitution provides for one Comptroller and Auditor General of India, so the office is held by a single person and not by a panel. The President appoints him by warrant under his hand and seal, he holds office for six years or till the age of 65, whichever comes first, and he can be removed only in the same manner as a judge of the Supreme Court, which protects his independence. He audits the accounts of the Union and the states, and his reports are laid before Parliament or the state legislature, where the Public Accounts Committee examines them. Options A, B and D are wrong because the CAG has never been a two-member, three-member or six-member body; only one officer holds the post, helped by the Indian Audit and Accounts Department. Exam tip: the CAG under Article 148 is a single-member office, while the Election Commission and the UPSC are multi-member bodies.

The correct answer is A, 919. The final figures of Census 2011 put the child sex ratio, counted for the age group 0 to 6 years, at 919 females per 1000 males. This was the lowest child sex ratio recorded since independence and a fall from 927 in the 2001 census, even though the overall sex ratio improved in the same decade from 933 to 943. The gap points to sex selection before birth and to poorer care of girl children, which is why the Pre-Conception and Pre-Natal Diagnostic Techniques Act and the Beti Bachao Beti Padhao scheme focus on it. Haryana recorded the lowest child sex ratio among the states and Kerala the highest overall sex ratio at 1084. Option B, 909, is below any census figure for this group. Option C, 929, is close to the 2001 figure of 927 but not the 2011 one. Option D, 939, is nearer the overall sex ratio than the child figure. Exam tip: Census 2011 means overall sex ratio 943 and child sex ratio 919.

The correct answer is C, Glycogen. The carbohydrates in our food are broken down into glucose, and the glucose that the body does not need at once is stored as glycogen, a branched chain of glucose units kept mainly in the liver and the skeletal muscles. It is often called animal starch. When blood sugar falls, hormones such as glucagon and adrenaline make the liver break glycogen down and release glucose, which is why a fasting body can keep working for hours. Extra energy beyond what glycogen stores can hold is turned into fat. Option A is wrong because maltose is a double sugar formed while starch is being digested and it is not a store. Option B is wrong because glucose is the form that circulates in the blood and is used at once, not the stored form. Option D is wrong because starch is the storage carbohydrate of plants, not of animals. Exam tip: plants store starch, animals store glycogen in the liver and muscles.

The correct answer is B, hydrogen. Soil acidity is measured on the pH scale, and pH depends on the concentration of hydrogen ions in the soil water. The more hydrogen ions there are, the lower the pH and the more acidic the soil. A pH below 7 is acidic, 7 is neutral and above 7 is alkaline, and most crops grow best between about 6 and 7.5. Acidic soils are common in areas of heavy rainfall, where water washes away bases such as calcium and magnesium, and they are corrected by adding lime, that is calcium carbonate. Option A is wrong because phosphorus is a plant nutrient whose shortage stunts growth but does not define acidity. Option C is wrong because oxygen in soil pores affects aeration and root respiration, not pH. Option D is wrong because nitrogen is a nutrient taken up as nitrate or ammonium and acidity is still read from hydrogen ions. Exam tip: pH measures hydrogen ions, below 7 is acidic, and lime cures an acidic soil.

The correct answer is C, decibel. The loudness or intensity level of sound is measured in decibels (dB), a unit named after Alexander Graham Bell. The decibel is a logarithmic unit, so every rise of 10 dB means the intensity of the sound has become ten times greater; that is why a whisper of about 30 dB and ordinary talk of about 60 dB feel so far apart. City traffic runs at about 80 dB, a sound above 120 dB is painful to the ear, and India's noise pollution rules are themselves written in dB for day and night limits. Option A is wrong because the hertz measures frequency, the number of vibrations a second, which the ear hears as pitch and not as loudness. Option B is wrong because wave number counts how many waves fit into a unit length and is used in spectroscopy, not for measuring sound. Option D is wrong for the same reason, since cm -1 is only the unit in which wave number is written. Exam tip: pitch goes with hertz, loudness with decibel.

The correct answer is A, Death. In early Buddhist art the Buddha was never shown in human form, so the events of his life were carved as symbols, and the stupa stands for his mahaparinirvana, that is his death at Kushinagar. A stupa is a domed mound raised over relics; Ashoka is said to have built many of them, and those at Sanchi, Bharhut and Amaravati are the best known. This code of symbols is fixed, and examiners return to it again and again. Option B is wrong because the first sermon at Sarnath is shown by the wheel, the dharmachakra, usually with two deer beside it for the deer park. Option C is wrong because the birth at Lumbini is shown by the lotus and the bull. Option D is wrong because the great departure from home is shown by a horse, while enlightenment at Bodh Gaya is shown by the Bodhi tree. Exam tip: lotus for birth, horse for renunciation, Bodhi tree for enlightenment, wheel for the first sermon and stupa for death.

The correct answer is C, 45 degree with the ground. Once the athlete's feet leave the ground they move as a projectile, and the horizontal distance covered, called the range, is given by R equal to u squared into sin 2 theta divided by g. The range is largest when sin 2 theta has its greatest value of one, which happens when 2 theta is 90 degrees, so the angle of projection theta must be 45 degrees. The same formula shows that two angles adding up to 90 degrees give equal ranges. Option A is wrong because a take-off straight up at 90 degrees sends the jumper vertically and the range falls to zero, though the height is the greatest. Option B is wrong because 60 degrees buys height at the cost of distance. Option D is wrong because 30 degrees keeps the jump flat and short, and it covers exactly the same distance as 60 degrees. Exam tip: maximum range at 45 degrees, maximum height at 90 degrees, and complementary angles share a range.

The correct answer is A, Jhumpa Lahiri. Jhumpa Lahiri, born in London to Bengali parents and brought up in the United States, moved to Rome and began writing in Italian rather than in English. Her Italian work includes the memoir In Altre Parole, published in English as In Other Words, and the novel Dove mi trovo, which she later put into English herself as Whereabouts. She first won fame in English with Interpreter of Maladies, the story collection that took the Pulitzer Prize in 1999, and with the novel The Namesake. Option B is wrong because Vikram Seth writes in English, as in A Suitable Boy and the verse novel The Golden Gate. Option C is wrong because Kiran Desai writes in English and won the Booker Prize in 2006 for The Inheritance of Loss. Option D is wrong because Arundhati Roy also writes in English, as in The God of Small Things. Exam tip: tie Jhumpa Lahiri to Interpreter of Maladies, the Pulitzer of 1999 and her later Italian books.

The correct answer is D, Punjabi. The Jammu and Kashmir Official Languages Act, 2020 gives the union territory five official languages: Kashmiri, Dogri, Urdu, Hindi and English. Punjabi is spoken in parts of the region, but it was not put on that list, so it is the odd one out. Before this law Urdu alone was the official language of the old state, even though hardly any household used it as a mother tongue, and the change was made so that the languages people actually speak would be used in government work. Option A is wrong because Hindi is one of the five named in the Act. Option B is wrong because Dogri, spoken mainly in the Jammu division, is both an official language of the union territory and a language of the Eighth Schedule of the Constitution. Option C is wrong because Urdu is official and was in fact the only official language earlier. Exam tip: remember the five as Kashmiri, Dogri, Urdu, Hindi and English.

The correct answer is C, Oersted. In 1820 the Danish scientist Hans Christian Oersted saw that a compass needle kept near a wire swung aside the moment a current flowed through the wire, and swung the other way when the current was reversed. That small observation proved that an electric current sets up a magnetic field around itself, which is the magnetic effect of current, and it opened the whole study of electromagnetism. The CGS unit of magnetising field strength, the oersted, carries his name. Option A is wrong because James Clerk Maxwell came later and gathered the laws of electricity and magnetism into four equations, showing that light itself is an electromagnetic wave. Option B is wrong because John Ambrose Fleming only gave the left hand and right hand rules, which tell us the direction of the force or of an induced current. Option D is wrong because Michael Faraday discovered electromagnetic induction in 1831, the opposite effect. Exam tip: Oersted 1820, current makes magnetism; Faraday 1831, magnetism makes current.

The correct answer is B, Kesavananda Bharati vs. State of Kerala. In this case of 1973 a bench of thirteen judges, the largest the Supreme Court has ever assembled, held by seven votes to six that Parliament may amend any part of the Constitution but may not damage or destroy its basic structure. Features such as the supremacy of the Constitution, the republican and democratic form of government, secularism, the separation of powers, judicial review and free and fair elections have since been treated as part of that basic structure. Option A is wrong because Golaknath (1967) took a different line altogether, holding that Parliament could not amend fundamental rights at all, and that ruling was itself overturned in Kesavananda. Option C is wrong because Minerva Mills (1980) only applied the doctrine that already existed and used it to strike down parts of the 42nd Amendment. Option D is wrong because a single case laid the doctrine down. Exam tip: Golaknath 1967, Kesavananda 1973, Minerva Mills 1980.

The correct answer is A, Poise. Dynamic viscosity measures how strongly a fluid resists flowing, and in the centimetre gram second system it is measured in poise, a unit named after the French physician Jean Louis Marie Poiseuille, who studied the flow of blood in narrow tubes. One poise is one dyne second per square centimetre, and since the SI unit is the pascal second, one pascal second equals ten poise. Thin liquids are usually quoted in centipoise: water at room temperature is about one centipoise while honey runs into thousands. Option B is wrong because the pascal second is the SI unit of dynamic viscosity, and the question asks for the CGS unit. Option C is wrong because the stoke is the CGS unit of kinematic viscosity, which is dynamic viscosity divided by density. Option D is wrong because option A already names the right unit. Exam tip: dynamic viscosity in poise and pascal second, kinematic viscosity in stoke and square metre per second.

The correct answer is B, no external forces act on the system. The law of conservation of linear momentum follows straight from Newton's second law: the rate of change of the momentum of a system equals the net external force acting on it, so when that force is zero the total momentum stays the same in size and in direction. The forces the bodies exert on one another are internal, they come in action and reaction pairs, and they cancel out, which is why a gun and its bullet, or two carrom coins that strike each other, keep the same total momentum. Option A is wrong because gravity is itself an external force and it changes the momentum of a falling body every second. Option C is wrong because kinetic energy is lost in an inelastic collision while momentum is still conserved, so the two are separate laws. Option D is wrong because option B states the condition correctly. Exam tip: momentum is conserved in every collision, kinetic energy only in a perfectly elastic one.

The correct answer is A, Irula. The Irula, also written Irular, are one of the main tribal communities of Tamil Nadu and live mostly in the Nilgiri hills and in the districts along the border with Kerala. They speak Irula, a Dravidian tongue close to Tamil, and are known across the country as expert snake and rat catchers; their cooperative society in Chennai supplies the venom from which antivenom is made. They are counted among the particularly vulnerable tribal groups of the state, along with the Toda, Kota and Kurumba of the same hills. Option B is wrong because no tribe of that name is recorded in Tamil Nadu. Option C is wrong because the Garo are a major tribe of Meghalaya in the north east and live in the Garo hills. Option D is wrong because the Khond, written here in a shortened form, are a tribe of Odisha known for hill cultivation. Exam tip: Irula and Toda with Tamil Nadu, Garo and Khasi with Meghalaya, Khond with Odisha.

The correct answer is C, 100%. India allows foreign direct investment of up to 100 per cent through the automatic route in railway infrastructure. The sector was opened in 2014, and the list covers suburban corridors taken up as public private partnerships, high speed train projects, dedicated freight lines, the making of rolling stock such as coaches, locomotives and train sets, railway electrification, signalling systems, freight and passenger terminals and mass rapid transport systems. Automatic route means the investor needs no prior approval from the government and only reports the investment to the Reserve Bank. Running the railways themselves remains with Indian Railways; only the infrastructure listed above is open. Option A is wrong because 50 per cent has never been the ceiling for this sector. Option B is wrong because 75 per cent belongs to no railway rule. Option D is wrong because railway infrastructure is not a prohibited sector, unlike lottery, gambling, chit funds, atomic energy and cigarette manufacture. Exam tip: railway infrastructure 100 per cent automatic, defence 74 per cent automatic.

The correct answer is B, the wire will not experience any force at all. The force on a current carrying conductor kept in a magnetic field is given by F equal to B I L sin theta, where theta is the angle between the direction of the current and the direction of the field. When the wire lies along the lines of force that angle is zero, sin theta becomes zero, and the force disappears however strong the field or the current may be. The same formula shows that the force is greatest when the wire is at right angles to the field, because sin theta is then one. Option A is wrong because the force, when there is one, never acts along the field; Fleming's left hand rule places it at right angles to both the field and the current. Option C is wrong for the same reason, as no rule gives a force pointing against the field. Option D is wrong here only because the angle is zero and no force arises at all. Exam tip: parallel means no force, perpendicular means maximum force.

The correct answer is D, the speed is less than the square root of 2gh. A body that slides down a smooth slope turns all of its potential energy mgh into translational kinetic energy and reaches the bottom with a speed equal to the square root of 2gh. A cylinder that rolls without slipping must also spin, so the same mgh has to be shared between translation and rotation, and the speed of its axis is bound to come out smaller. Working it out for a solid cylinder, mgh equals half m v squared plus one fourth m v squared, which gives v as the square root of four gh by three, about 1.15 times the square root of gh against 1.41 for the sliding body. Option A is wrong because gh is not even a speed, as the units do not match. Option B is wrong because mgh is an energy and the mass cancels out in any case. Option C is wrong because that value belongs to a body that slides without rotating. Exam tip: of bodies rolling down the same slope, a solid sphere beats a solid cylinder, which beats a ring.

The correct answer is A, Photosynthesis. Green plants give out oxygen only during photosynthesis, the process in which they use light energy to make their own food.

In photosynthesis a green leaf takes in carbon dioxide through its stomata and water through the roots, and in the presence of sunlight and chlorophyll turns them into glucose. The oxygen that comes out is a by-product, and it comes from the splitting of water molecules, not from carbon dioxide. This is the process that keeps the oxygen of the atmosphere topped up, which is why forests are called the lungs of the planet.

Option B is wrong because respiration does the opposite: it uses up oxygen and gives out carbon dioxide. Option C is wrong because transpiration is the loss of water as vapour from the leaves, not of oxygen. Option D is wrong because excretion is the removal of waste from the body and releases no oxygen.

Exam tip: photosynthesis takes in CO2 and gives out O2; respiration takes in O2 and gives out CO2.

The correct answer is C, Using trees or large shrubs as fences for a garden. A line of trees or tall shrubs works as a windbreak: it slows the wind close to the ground so the moving air can no longer lift loose soil.

Wind erosion happens on dry, bare, open land where the topsoil is loose and there is no cover to hold it. Rows of trees planted across the direction of the wind are called shelterbelts, and they are the standard remedy in dry regions such as western Rajasthan, where they were planted along the Indira Gandhi Canal. The roots of the trees also bind the soil and their fallen leaves add humus to it.

Option A is wrong because paving land with tiles or cement seals the soil and destroys its use for plants; it is not soil conservation. Option B is wrong because crop rotation restores soil fertility rather than blocking the wind. Option D is wrong because growing vegetables in pots at home does nothing for open land.

Exam tip: shelterbelts and windbreaks check wind erosion; contour ploughing and terracing check water erosion.

The correct answer is D, Sindhi. Sindhi was added to the Eighth Schedule of the Constitution by the 21st Constitutional Amendment Act of 1967.

The Eighth Schedule is the list of languages the Constitution recognises, and a candidate may take the civil services examination in any of them. It began in 1950 with 14 languages. Sindhi came in as the fifteenth in 1967, after Partition brought a large Sindhi-speaking population into India without a state of its own. Konkani, Manipuri and Nepali were added together by the 71st Amendment in 1992, and Bodo, Dogri, Maithili and Santhali by the 92nd Amendment in 2003, which took the list to 22 languages.

Option A is wrong because Manipuri was added in 1992. Option B is wrong because Nepali also came in 1992. Option C is wrong because Konkani was part of the same 1992 group.

Exam tip: 21st Amendment 1967 gave Sindhi; 71st in 1992 gave Konkani, Manipuri and Nepali; 92nd in 2003 gave Bodo, Dogri, Maithili and Santhali.

The correct answer is C, 100%. India allows 100 per cent foreign direct investment through the automatic route in the construction, operation and maintenance of rail infrastructure projects.

This opening was announced in 2014 and covers suburban corridors taken up through public private partnership, high speed train projects, dedicated freight lines, rolling stock factories, railway electrification, signalling systems, freight terminals and passenger terminals. Automatic route means the investor needs no prior approval from the government or the Reserve Bank of India and only files the required reports after the money comes in. Train operations themselves stay with Indian Railways, so the investment goes into building and maintaining the assets.

Option A is wrong because there is no 49 per cent ceiling on rail infrastructure. Option B is wrong because 74 per cent is a partial cap used in some other sectors, not here. Option D is wrong because 80 per cent is not a limit used anywhere in India's FDI policy.

Exam tip: rail infrastructure takes 100 per cent FDI on the automatic route, while running the trains stays with Indian Railways.

The correct answer is B, Papaya. Papaya is raised from seed, so it is not multiplied by vegetative propagation the way the other three plants are.

Vegetative propagation means growing a new plant from a vegetative part of the parent, such as a stem, root, leaf or bud, without seeds. Because no seed is involved, the new plant is a copy of the parent and it also fruits sooner. Papaya has plenty of viable seed, and its soft unbranched stem does not strike roots from a cutting, so nurseries sow seed instead.

Option A is wrong because rose is the standard example of a plant grown from stem cuttings. Option C is wrong because banana is grown from suckers that come up from the underground stem, as its seeds are sterile. Option D is wrong because orange and other citrus plants are multiplied by budding and grafting on a rootstock.

Exam tip: cuttings give rose and sugarcane, suckers give banana, grafting and budding give citrus and mango, while papaya comes from seed.

The correct answer is A, Cellulose and Pectin. Collenchyma cells lay down extra cellulose and pectin at the corners of their walls, which makes the tissue strong and yet flexible.

Collenchyma is a simple permanent tissue of plants, found just under the epidermis in the stems and leaf stalks of dicot plants and in the midrib of a leaf. Its cells are living and elongated, thickened unevenly at the corners, with almost no space between them. This uneven thickening lets a young shoot or a leaf stalk bend in the wind without breaking, and it is what allows climbing stems to twist.

Option B is wrong because lignin thickens sclerenchyma and cutin waterproofs the epidermis. Option C is wrong because chitin is found in fungal walls and insect skeletons, not in plant tissue. Option D is wrong because suberin is deposited in cork cells.

Exam tip: parenchyma has thin cellulose walls, collenchyma adds cellulose and pectin at the corners and stays flexible, sclerenchyma is lignified, dead and rigid.

The correct answer is B, Hydra. Hydra is the one animal in the list that reproduces both by budding and by regeneration.

In budding, a bulge grows out from the body wall of the parent Hydra, develops a mouth and tentacles, and then breaks off as a small independent Hydra. In regeneration, a piece cut from the body grows the missing parts back and becomes a complete animal, because Hydra keeps a large store of unspecialised cells that can turn into any tissue. Both are forms of asexual reproduction, so the young are copies of the parent.

Option A is wrong because Planaria is the classic example of regeneration alone and does not bud. Option C is wrong because Amoeba divides into two by binary fission. Option D is wrong because yeast reproduces only by budding, and it is a fungus, not an animal.

Exam tip: Hydra shows budding and regeneration, Planaria only regeneration, Amoeba binary fission, Plasmodium multiple fission.

The correct answer is D, Karnataka. The Kolar Gold Fields lie in the Kolar district of Karnataka, on the Dharwar rocks of the peninsular plateau.

Kolar was for a long time India's main source of gold and one of the deepest mines in the world, going down about three kilometres. Mining stopped in 2001 because the ore left was poor and the cost of working at that depth had become too high. Karnataka also has the Hutti gold mines in Raichur district, which still work, and the state leads India in gold production. The town of Kolar grew around the mines and once drew its electricity from the Shivanasamudra power station, among the earliest hydel supplies in Asia.

Option A is wrong because Madhya Pradesh is known for diamonds at Panna. Option B is wrong because Andhra Pradesh has no Kolar field. Option C is wrong because Tamil Nadu is known for lignite at Neyveli.

Exam tip: gold in Karnataka means Kolar and Hutti; Kolar closed in 2001 and Hutti still works.