CDS 2023 Previous Year GK Questions with Answers

The correct answer is C, Blue. A leaf from a sunny day is full of starch made by photosynthesis, and iodine turns starch blue-black.

This is the standard school test for starch in a leaf. Boiling the leaf in water kills its cells and softens it so that the solutions can enter. Boiling it in alcohol, usually over a water bath because alcohol catches fire easily, dissolves the chlorophyll, leaving the leaf pale or nearly colourless. When iodine solution is then added, the starch stored in the leaf reacts with it and the leaf turns blue-black. A leaf kept in the dark for two days before the test shows no blue colour, proving that light is needed for photosynthesis.

A is wrong: the leaf is colourless only before iodine is added; the starch then turns it blue.

B is wrong: the green chlorophyll has already been removed by the boiling alcohol.

D is wrong: a starch-free leaf would show the brown colour of iodine, not white, and this leaf has starch.

Exam tip: iodine test: starch gives blue-black; alcohol removes chlorophyll before the test.

The correct answer is A, greater than the speed of sound. A body moving faster than sound outruns its own sound waves, which pile up into a shock wave heard on the ground as a sonic boom.

In air at room temperature, sound travels at about 343 m/s. A supersonic jet or a bullet moving faster than this leaves its sound waves behind, and they bunch together into a cone-shaped shock wave trailing the object. When the edge of this cone sweeps over a listener, the sudden change in air pressure is heard as a loud bang, strong enough to rattle or even crack window glass. Speeds are often given as a Mach number, the ratio of the object's speed to the speed of sound, so supersonic means Mach 1 or more.

B is wrong: no material object can travel faster than light.

C is wrong: below the speed of sound the waves spread ahead of the source, so no shock wave forms.

D is wrong: at exactly the speed of sound the waves bunch up at the nose, but the boom heard on the ground comes from supersonic flight.

Exam tip: Mach 1 = speed of sound; above Mach 1 is supersonic and above Mach 5 hypersonic.

The correct answer is A, lactic acid. During a hard sprint the muscles run short of oxygen and switch to anaerobic respiration, which leaves lactic acid behind.

In every cell, glucose is first broken down into pyruvic acid by glycolysis. When oxygen is plentiful, pyruvic acid is fully oxidised to carbon dioxide and water in the mitochondria, releasing a lot of energy. During intense exercise the blood cannot bring oxygen fast enough, so muscle cells turn pyruvic acid into lactic acid to keep producing a little energy quickly. The build-up of lactic acid is linked with the cramps and burning pain felt after a sprint; rest and deep breathing let the body clear it.

B is wrong: carbon dioxide is a product of aerobic respiration and is removed through the lungs, so it does not collect in the muscles.

C is wrong: pyruvic acid is only an intermediate; in oxygen shortage it is converted to lactic acid rather than piling up.

D is wrong: ethanol is made by anaerobic respiration in yeast, not in human muscle.

Exam tip: no oxygen in muscle gives lactic acid; no oxygen in yeast gives ethanol and CO2.

The correct answer is D, increase to four times of its original value. Gravitational force varies inversely as the square of the distance, so halving the distance makes the force 2 × 2 = 4 times larger.

Newton's law of universal gravitation says F = G m₁m₂ / r², where m₁ and m₂ are the two masses, r is the distance between their centres and G is the universal gravitational constant. The masses of the Earth and the Moon do not change here, so only r matters. Replacing r with r/2 puts (r/2)² = r²/4 in the denominator, and dividing by a quarter multiplies the force by four. Likewise, doubling the distance would cut the force to one quarter.

A is wrong: halving the force would need the distance to grow, not shrink, and by a factor of √2.

B is wrong: a doubling would hold only if force varied inversely with distance, not with its square.

C is wrong: the force depends on distance, so it cannot stay the same when the distance changes.

Exam tip: inverse-square law: distance ½ gives force ×4; distance ×3 gives force ⅑.

The correct answer is A, Punjab and Sind. The elections of 1937 were held under the Government of India Act, 1935, and the Congress swept the country, winning a clear majority in five provinces and emerging as the largest party in most of the rest. The two provinces where it did not come first were Punjab and Sind. In Punjab the Unionist Party of Sikandar Hyat Khan, a cross-community alliance of landlords, dominated the assembly. In Sind local parties and independents held the field and no single group was strong, so the Congress stayed a minor player. The Congress eventually formed ministries in eight of the eleven provinces, and these resigned in October 1939 over India being drawn into the Second World War without consultation. Option B is wrong because the Congress was the largest party in Assam. Options C and D are wrong for the same reason, as each of them wrongly names Assam. Exam tip: 1937 elections - Congress ministries in 8 of 11 provinces, with Punjab and Sind the exceptions.

The correct answer is B, Opening of soda bottle. Nothing is oxidised when a soda bottle is opened; the pressure inside simply falls, the dissolved carbon dioxide becomes less soluble and escapes as bubbles. That is a physical change governed by Henry's law, not a chemical reaction, because the carbon dioxide molecules are unchanged. Oxidation, by contrast, means a substance gains oxygen or loses electrons. Option A is wrong because rusting is oxidation: iron reacts with oxygen and moisture to form hydrated iron oxide, the reddish-brown rust. Option C is wrong because rancidity is the oxidation of fats and oils in food, which gives the stale smell and taste, and is slowed by airtight packing, refrigeration, nitrogen flushing or antioxidants. Option D is wrong because combustion is rapid oxidation with heat and light, as when a fuel burns in air. Exam tip: a change is chemical only when a new substance is formed, so dissolving and fizzing are physical while rusting, rancidity and burning are oxidation.

The correct answer is B, there is incomplete combustion. Naphthalene is an aromatic hydrocarbon, C10H8, with a very high proportion of carbon, so the air around the flame cannot supply enough oxygen to burn all of it to carbon dioxide. The unburnt carbon leaves the flame as glowing soot particles, which is what makes the light yellow and the smoke black. This is the general rule for unsaturated and aromatic compounds, while saturated hydrocarbons burn with a clean blue flame. The same chemistry explains why a kerosene lamp smokes and why the air holes of a gas burner are opened to get a blue flame. Option A is wrong because the carbon to hydrogen ratio in naphthalene is high, not low, and that is precisely the cause. Option C is wrong because excess air would give complete combustion and a clean flame. Option D is wrong because sooty burning comes from carbon itself, not from nitrogen or sulphur impurities. Exam tip: saturated compounds give a blue flame, unsaturated and aromatic ones a yellow sooty flame.

The correct answer is B, Assam Rifles. It is the only such force whose administrative control lies with the Ministry of Home Affairs while its operational control lies with the Indian Army. The Assam Rifles is also India's oldest paramilitary force, raised in 1835 as the Cachar Levy to guard British tea estates and settlements in the North East. Most of its officers come on deputation from the Army; it guards the India–Myanmar border and runs counter-insurgency operations in the North East, which is why it is called the Sentinels of the North East and the Friends of the Hill People. A is wrong, because the CRPF, India's largest central armed police force, is fully under the Home Ministry. C is wrong, because the ITBP, raised in 1962 to guard the border with China, is also under the Home Ministry alone. D is wrong, because the CISF, set up in 1969 to protect industrial units, airports and metros, reports only to the Home Ministry. Exam tip: Assam Rifles, raised 1835, Home Ministry for administration and Army for operations, guards the Myanmar border.

The correct answer is A, 1 only. Statement 1 is true and statement 2 is false. Race to Zero is a global campaign backed by the United Nations and launched in 2020, ahead of the COP26 climate talks in Glasgow. It rallies businesses, cities, regions, investors and universities to take rigorous action to halve global emissions by 2030 and reach net-zero emissions by 2050 at the latest, in line with the Paris Agreement aim of limiting warming to 1.5 degrees Celsius. Building momentum for a shift to a decarbonised economy is exactly its aim, so statement 1 is correct. Statement 2 is wrong: the zero in the name means net-zero carbon emissions, not a zero-sum game, where one side's gain equals the other side's loss; climate action is meant to benefit everyone. B is wrong, because statement 2 is the false one. C is wrong, because it accepts the false zero-sum statement. D is wrong, because statement 1 correctly describes the campaign. Exam tip: Race to Zero, UN-backed, 2020, halve emissions by 2030, net zero by 2050.

The correct answer is B, Vote on Account. It is the advance grant the Lok Sabha makes so that the government can keep spending from 1 April until the full budget is passed. Article 116 of the Constitution allows it. No money can leave the Consolidated Fund of India without Parliament's approval, so this grant fills the gap. It usually covers two months, about one-sixth of the year's estimates. Since the budget moved to 1 February in 2017, it is mostly seen in election years, when the outgoing government leaves the full budget to the new Lok Sabha. A is wrong, because a vote of credit, also under Article 116, is a blank-cheque grant for an unexpected need that cannot be stated in detail. C is wrong, because the Appropriation Bill under Article 114 authorises withdrawal from the Consolidated Fund after the demands are voted. D is wrong, because advance account is not a budget term of the Constitution. Exam tip: vote on account keeps the government running, vote of credit is the blank cheque; both sit in Article 116.

The correct answer is B, Tendulkar Committee. The expert group headed by Suresh Tendulkar, which reported in 2009, recommended measuring poverty through MPCE on the Mixed Reference Period. Under this method, spending on five rarely bought items, namely clothing, footwear, durable goods, education and institutional medical care, is recorded over the last 365 days, and all other items over the last 30 days. Tendulkar also moved away from the old calorie norm and used one poverty line basket for rural and urban India, covering spending on health and education. By this method, India's poverty ratio came to 21.9 per cent in 2011-12. A is wrong, because the Lakdawala group of 1993 used the Uniform Reference Period and state-wise poverty lines. C is wrong, because the Dandekar and Rath study of 1971 based poverty on an intake of 2,250 calories a day. D is wrong, because the Alagh task force of 1979 fixed calorie norms of 2,400 rural and 2,100 urban. Exam tip: Alagh 1979 calories, Lakdawala 1993 URP, Tendulkar 2009 MRP, Rangarajan 2014.

The correct answer is A, crowding out. When the government runs a deficit, it borrows heavily from the same pool of savings that private firms use, so interest rates rise and private investment falls. This squeezing out of private spending by public borrowing is called the crowding out effect. It is the main argument against high fiscal deficits: if the state absorbs most of the savings, businesses find loans costlier and invest less, and the boost from government spending is partly cancelled. It is also why India's fiscal rules, such as the FRBM Act, 2003, aim to keep the deficit in check. B is wrong, because crowding in is the opposite, when public spending on roads, ports and the like encourages more private investment. C is wrong, because pump priming means government spending during a slump to restart demand, not the fall in private investment. D is wrong, because dumping is selling exports abroad below their home price or cost, a trade issue met with anti-dumping duty. Exam tip: deficit borrowing, higher interest rates, less private investment; that is crowding out.

The correct answer is D, Krishna and Tungabhadra. Going south from Gulbarga you first cross the Krishna and then reach the Tungabhadra, on whose south bank Hampi stands. The land between these two rivers is the Raichur Doab, a fertile tract that the Bahmani Sultanate and the Vijayanagara Empire fought over for nearly two centuries. Gulbarga, now Kalaburagi, was the first Bahmani capital from 1347, while Hampi was the capital of Vijayanagara, founded in 1336. The Tungabhadra is itself a tributary of the Krishna and joins it further east, near Kurnool. A is wrong, because the Narmada flows far to the north through central India, and the Godavari also lies north of Gulbarga. B is wrong, because the Mahanadi drains Chhattisgarh and Odisha, far from this region. C is wrong, because the Kaveri flows well south of Hampi and the Periyar is a river of Kerala. Exam tip: the Raichur Doab lies between the Krishna and the Tungabhadra; Hampi is on the Tungabhadra.

The correct answer is D, 1, 2 and 3. All three statements are true. Statement 1: the size of an eruption is rated on the Volcanic Explosivity Index, a scale from 0 to 8 based on the volume of material thrown out and the height of the eruption column; each step up means roughly ten times more material. Statement 2: Iceland sits on the Mid-Atlantic Ridge where two plates move apart, and the Philippines lies on the Pacific Ring of Fire, so both were built by volcanic activity. Statement 3: volcanic ash and lava weather into deep, mineral-rich soils, which is why Java in Indonesia supports dense farming and the Deccan's black soil, formed from basalt lava, grows cotton so well. A is wrong, because it leaves out statement 3, which is true. B is wrong, because it drops statement 1, and the index is the standard measure. C is wrong, because it drops statement 2, though both Iceland and the Philippines are volcanic. Exam tip: VEI runs from 0 to 8; Iceland sits on a ridge, the Philippines on the Ring of Fire; basalt gives black soil.

The correct answer is B, 2 and 6. The Tropic of Cancer crosses eight Indian states, and only two of them touch the sea. Running at about 23.5 degrees north, it passes from west to east through Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, West Bengal, Tripura and Mizoram. Gujarat and West Bengal have coastlines, while the other six are landlocked. The line divides India into two nearly equal halves, with the northern part in the temperate zone and the southern part in the tropical zone. A is wrong, because two coastal states, not one, lie on the line, and the total is eight. C is wrong, because 2 and 5 makes only seven states and misses one of the six landlocked ones. D is wrong, because no third coastal state such as Odisha lies on the Tropic; Odisha lies south of it. Exam tip: Tropic of Cancer, eight states from Gujarat to Mizoram; the coastal pair is Gujarat and West Bengal.

The correct answer is D, The Treaty of Salbai. Signed in May 1782 between the East India Company and the Marathas, it ended the First Anglo-Maratha War that had begun in 1775. The war started when the Bombay government backed Raghunathrao's claim to the Peshwa's seat. Mahadji Scindia helped broker the peace at Salbai: the British kept Salsette, recognised the young Madhavrao II as Peshwa, and Raghunathrao was pensioned off. The treaty brought about twenty years of peace between the two powers. A is wrong, because the Treaty of Surat of 1775 between the British and Raghunathrao started the war rather than ending it. B is wrong, because the Treaty of Purandar of 1776, made by the Calcutta council with the Poona ministers, set Surat aside but did not end the fighting. C is wrong, because the Convention of Wadgaon of 1779 was a humiliating surrender by a British force, later rejected by Warren Hastings. Exam tip: Surat 1775 began it, then Purandar 1776 and Wadgaon 1779, and Salbai 1782 ended it.

The correct answer is B, The Battle of Colachel. At Colachel in August 1741, Marthanda Varma of Travancore defeated the Dutch East India Company. It was one of the rare times an Indian ruler decisively beat a European power in open battle, and it ended Dutch hopes of expanding on the Malabar coast. The Dutch commander Eustachius De Lannoy was captured, joined Travancore's service, trained its army on European lines and rose to be its chief commander. Colachel lies on the coast of today's Kanyakumari district in Tamil Nadu. A is wrong, because at Porto Novo in 1781 the British under Eyre Coote defeated Hyder Ali in the Second Anglo-Mysore War. C is wrong, because the battles of Pollilore were fought in 1780 and 1781 between Hyder Ali and the British in that same war. D is wrong, because Changanacherry is a town in central Kerala, not the scene of the 1741 fight with the Dutch. Exam tip: Colachel 1741, Marthanda Varma beat the Dutch; Porto Novo 1781, Eyre Coote beat Hyder Ali.

The correct answer is C, The Estimates Committee. All its 30 members are elected by the Lok Sabha alone, so the Rajya Sabha has no seat on it. The Estimates Committee examines the budget estimates and suggests economies in expenditure, which is why it is called a continuous economy committee. It is the largest financial committee of Parliament; its members are elected every year by proportional representation through the single transferable vote, and a minister cannot be a member. The point that sticks: money matters belong to the Lok Sabha, so the Rajya Sabha is kept out of this one. A is wrong, because the Public Accounts Committee has 22 members, 15 from the Lok Sabha and 7 from the Rajya Sabha. B is wrong, because the Committee on Public Undertakings also has 15 Lok Sabha and 7 Rajya Sabha members. D is wrong, because the committee on SC and ST welfare has 20 Lok Sabha and 10 Rajya Sabha members. Exam tip: Estimates 30, all Lok Sabha; PAC and Public Undertakings, 15 plus 7.

The correct answer is C, The post of the SGI is a constitutional post. It is the one false statement, because the Constitution creates only the Attorney General, not the Solicitor General. Article 76 provides for the Attorney General for India, the chief legal advisor to the Government and the highest law officer. The Solicitor General is the second law officer who assists the Attorney General; the post rests on the Law Officers (Conditions of Service) Rules, 1987, so it is a non-constitutional post. The detail that sticks: only the Attorney General gets an Article number and, under Article 88, the right to speak in both Houses of Parliament. A is a true statement, since the chief legal advisor is the Attorney General, not the SGI. B is true, because the SGI ranks just below the Attorney General as the second law officer. D is true, as the Appointments Committee of the Cabinet appoints the SGI and the Additional Solicitors General. Exam tip: Attorney General, Article 76, constitutional; Solicitor General, no Article, non-constitutional.