UPSC Prelims PYQs with explanations
Real questions from official papers, mapped to syllabus topics. Attempt each one; the answer and the reason appear instantly.
With reference to solar water pumps, consider the following statements :
- 1. Solar power can be used for running surface pumps and not for submersible pumps.
- 2. Solar power can be used for running centrifugal pumps and not the ones with piston.
Which of the statements given above is/are correct ?
Answer (d) & explanation
Neither statement is correct (d). Statement 1 is wrong: solar panels can run both surface pumps, which lift water from ponds and canals, and submersible pumps, which sit inside a borewell. Statement 2 is wrong: solar power can run both centrifugal pumps and positive-displacement pumps, such as piston pumps. Each statement wrongly rules out one type; the pump type depends on the water depth and flow needed, not on the power source.
Notice PM-KUSUM (2019), which subsidises standalone solar pumps, solarisation of grid-connected pumps, and small solar plants on farmland. Solar pumps cut diesel use and power subsidies, but critics warn that free daytime power can lead to over-extraction of groundwater.
Answer as per the official UPSC answer key.
Consider the following arrangement that has some missing letters :
abab_b_bcb_dcdcded_d
The missing letters which complete the arrangement are
Answer (c) & explanation
The missing letters are a, c, c, e (c). Step 1: there are 20 letters. Split them into blocks of five: abab_ | b_bcb | _dcdc | ded_d. Step 2: each block alternates two letters: ababa, bcbcb, cdcdc, deded. Each new block moves one letter forward. Step 3: the blanks are a, c, c, e. That is option (c). Options (a), (b) and (d) break the alternating pattern.
Tip: count the total letters, then try equal blocks. A clean split (here 4 blocks of 5) usually shows the rule at once.
Answer as per the official UPSC answer key.
A shop owner offers the following discount options on an article to a customer :
- 1. Successive discounts of 10% and 20%, and then pay a service tax of 10%
- 2. Successive discounts of 20% and 10%, and then pay a service tax of 10%
- 3. Pay a service tax of 10% first, then successive discounts of 20% and 10%
Which one of the following is correct?
Answer (d) & explanation
All three options are equally good (d). Step 1: each option multiplies the price by the same three numbers: 0·9 (10% off), 0·8 (20% off) and 1·1 (10% tax). Step 2: multiplication can be done in any order: 0·9 × 0·8 × 1·1 = 0·8 × 0·9 × 1·1 = 1·1 × 0·8 × 0·9 = 0·792. Step 3: so the final price is the same in all three. Options (a), (b) and (c) fail.
Tip: successive percentage changes multiply, so their order never matters. Two successive discounts of 20% and 10% equal a single 28% discount, not 30%.
Answer as per the official UPSC answer key.
A vessel full of water weighs 40 kg. If it is one-third filled, its weight becomes 20 kg. What is the weight of the empty vessel?
Answer (a) & explanation
The empty vessel weighs 10 kg (a). Step 1: full weighs 40 kg; one-third full weighs 20 kg. Going from full to one-third full removes 2/3 of the water, and the weight drops by 40 − 20 = 20 kg. Step 2: so 2/3 of the water = 20 kg, and all the water = 30 kg. Step 3: vessel = 40 − 30 = 10 kg. Check: one-third water = 10 kg, plus vessel 10 kg = 20 kg. Options (b), (c) and (d) fail.
Tip: the difference between two states removes the vessel's weight. Use it to find the contents first, then subtract from the total.
Answer as per the official UPSC answer key.
With reference to the history of India, “Ulgulan” or the Great Tumult is the description of which of the following events ?
Answer (d) & explanation
Ulgulan describes Birsa Munda's revolt (d). Birsa Munda called on the Mundas of Chotanagpur to rise against landlords, moneylenders, missionaries and the British. They were destroying the khuntkatti system of communal land ownership and forcing beth begari (unpaid labour). Birsa also started a religious movement, calling himself a prophet. The rising of 1899–1900 is called the Ulgulan, or Great Tumult. Birsa died in Ranchi jail in June 1900, at about 25. The Chotanagpur Tenancy Act (1908) followed, banning the transfer of tribal land to outsiders. The 1857 revolt (a), the Mappila Rebellion (b) and the Indigo Revolt (c) are different events.
Notice that 15 November, his birthday, is Janjatiya Gaurav Divas. His 150th birth anniversary was marked in 2025.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. The weightage of food in Consumer Price Index (CPI) is higher than that in Wholesale Price Index (WPI).
- 2. The WPI does not capture changes in the prices of services, which CPI does.
- 3. Reserve Bank of India has now adopted WPI as its key measure of inflation and to decide on changing the key policy rates.
Which of the statements given above is/are correct ?
Answer (a) & explanation
Statements 1 and 2 are correct (a). Statement 1 is right because food has a weight of about 46% in CPI (Combined), but only about 24% in the WPI. Statement 2 is right because the WPI covers goods only, while the CPI includes services such as education, health, housing and transport. Statement 3 is wrong because, after the Urjit Patel Committee (2014), the RBI adopted CPI (Combined) as its key inflation measure, not WPI. Under flexible inflation targeting, the target is 4%, with a band of 2–6%.
Notice the agencies: the NSO (MoSPI) compiles CPI, and the Office of the Economic Adviser (DPIIT) compiles WPI. Both use the base year 2011–12 for WPI and 2012 for CPI, with revisions under way.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Jet streams occur in the Northern Hemisphere only.
- 2. Only some cyclones develop an eye.
- 3. The temperature inside the eye of a cyclone is nearly 10°C lesser than that of the surroundings.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Only statement 2 is correct (c). Statement 1 is wrong: jet streams blow in both hemispheres; the subtropical and polar-front jets circle each pole. Statement 2 is right: only mature, strong tropical cyclones develop a clear eye; weaker storms and temperate cyclones do not. Statement 3 is wrong: sinking air in the eye warms as it compresses, so the eye is warmer than its surroundings, by up to about 10 °C, not colder. The eye is calm, with light winds and clear skies, ringed by the violent eyewall.
Notice that the sub-tropical westerly jet shifting north of the Himalayas helps the Indian monsoon set in, and the tropical easterly jet blows over India in summer.
The 10 °C figure is real. Statement 3 is wrong because it says lesser instead of warmer.
Answer as per the official UPSC answer key.
Read the passage
In India, agriculture still engages about half of its workforce, and about 85 per cent of its farms are small and marginal. Compared to China and Vietnam, which have experienced fast structural and rural transformation, India’s story is of slow transformation. As a result, poverty reduction in India was at a much slower pace during 1988–2014, compared to China and Vietnam. India’s poverty reduction was slow during 1988–2005, but during 2005–2012, it accelerated dramatically—almost three times faster than during the earlier period. What did India do during this period? Research reveals that the relative price scenario changed significantly (by more than 50%) in favour of agriculture in the wake of rising global prices. This boosted private investments in agriculture by more than 50%. As a result, agri-GDP growth touched 4·1% during 2007–2012 as against 2·4% during 2002–2007. The net surplus of agri-trade touched $25 billion in 2013–2014; real farm wages rose by 7% per annum. All this led to unprecedented fall in poverty.
With reference to the above passage, the following assumptions have been made :
- 1. Structural and rural transformation is impossible when farms are mainly small and marginal.
- 2. A good price incentive can trigger investments in agriculture.
- 3. India needs to build value chains for high-value agri-products like livestock and horticulture.
- 4. Higher global prices of agricultural commodities are essential for India’s poverty reduction.
Which of the above assumptions are valid?
Answer (c) & explanation
Assumptions 2 and 3 are valid (c). Step 1: the passage says better relative prices raised private farm investment by over 50%. So a good price incentive triggers investment (2). Step 2: UPSC's key also reads into the price-led gains a need to build value chains for high-value products like livestock and horticulture (3). Step 3: assumption 1 says transformation is impossible with small farms; that is too strong. Assumption 4 says high global prices are essential for poverty reduction; also too strong. So options (a), (b) and (d) fail.
Tip: "impossible" and "essential" are absolute words. Unless the passage uses them, reject such statements.
Answer as per the official UPSC answer key.
For what value of n, the sum of digits in the number (10n + 1) is 2?
Answer (b) & explanation
The digit sum is 2 for any whole number n (b). Step 1: for n ≥ 1, 10ⁿ + 1 looks like 100…01: one 1, some zeros, then another 1. Digit sum = 2. Step 2: for n = 0, 10⁰ = 1, so 10⁰ + 1 = 2. Digit sum is also 2. Step 3: so it works for every whole number (0, 1, 2, …). Option (c) leaves out 0. Option (a) is too narrow. Option (d) fails because a fractional n, like 0·5, gives a non-whole number.
Tip: whole numbers include 0; natural (positive) numbers start at 1. CSAT often tests this difference, so always check n = 0 separately.
don't forget n = 0. That is the difference between (b) and (c).
Answer as per the official UPSC answer key.
A Parliamentary System of Government is one in which
Answer (b) & explanation
Option (b) defines a parliamentary system. Its key feature is responsible government: the executive stays in office only while it keeps the confidence of the legislature, and can be removed by a no-confidence motion. For the Union, Article 75(3) makes the Council of Ministers collectively responsible to the Lok Sabha. Option (a) is wrong because only the majority party or coalition forms the government. Option (c) describes a presidential system, as in the USA, where the people elect the executive. Option (d) is wrong because a fixed term with no removal is also a presidential feature.
India took this system from Britain. Notice the features: a nominal head (the President) and a real executive (the PM), and ministers drawn from Parliament.
(d) describes something close to a fixed-term system. "Cannot be removed" is the opposite of parliamentary rule.
Answer as per the official UPSC answer key.
In India, the term “Public Key Infrastructure” is used in the context of
Answer (a) & explanation
PKI refers to digital security infrastructure (a). Public Key Infrastructure is the system of encryption keys, digital certificates and certifying authorities that makes digital signatures and secure online transactions possible. Each user has a public key, which anyone can see, and a private key, kept secret. A certifying authority vouches that a public key belongs to a particular person. In India, the Controller of Certifying Authorities, under the IT Act, 2000, oversees PKI and runs the Root Certifying Authority of India. It has nothing to do with food (b), health and education (c), or transport (d).
Notice the everyday uses: Aadhaar eSign, income tax filing with digital signatures, e-tendering, and the HTTPS padlock on websites.
Answer as per the official UPSC answer key.
In rural road construction, the use of which of the following is preferred for ensuring environmental sustainability or to reduce carbon footprint ?
- 1. Copper slag
- 2. Cold mix asphalt technology
- 3. Geotextiles
- 4. Hot mix asphalt technology
- 5. Portland cement
Select the correct answer using the code given below :
Answer (a) & explanation
Copper slag, cold mix asphalt and geotextiles are preferred (a). Item 1 is right: copper slag reuses an industrial waste in place of natural sand and aggregate. Item 2 is right: cold mix asphalt is laid without heating, saving fuel and emissions, and it works in rain and cold hill areas. Item 3 is right: geotextiles, such as jute or coir mats, strengthen the road and control erosion with less material. Item 4 is wrong: hot mix asphalt needs heating to about 150 °C, which burns fuel. Item 5 is wrong: making Portland cement releases a lot of CO₂.
Notice PMGSY (Pradhan Mantri Gram Sadak Yojana, 2000), which promotes green technologies in rural roads, including waste plastic, fly ash and these materials.
Answer as per the official UPSC answer key.
Read the passage
Although most of the Genetically Modified (GM) crops cultivated now are genetically engineered for a single trait, in future, crops genetically engineered for more than one trait will be the norm. Thus, biotechnology’s role in agriculture and the regulation of the same cannot be understood solely in the context of the current generation of GM crops. Instead, there is a need to take a comprehensive look, taking into account various aspects, including socio-economic impacts, so that the potential of the technology can be harnessed while minimizing negative impacts. Given the importance of biotechnology in developing varieties that can help in climate change mitigation and adaptation, not using biotechnology as a part of the climate change action plan cannot be an option. Domestic regulation of biotechnology cannot be viewed in isolation of trade policy and obligations under various international treaties and conventions.
With reference to the above passage, the following assumptions have been made :
- 1. Biotechnology regulation is an evolving process.
- 2. Participation of people is needed in policy decisions regarding biotechnology regulation.
- 3. Biotechnology regulation should take into account socio-economic aspects in decision-making.
- 4. Wider involvement of political executive in biotechnology regulation improves its effectiveness in dealing with the country’s trade policies and international obligations.
Which of the above assumptions are valid?
Answer (b) & explanation
Assumptions 1 and 3 are valid (b). Step 1: the passage says regulation must look beyond "the current generation" of GM crops. So biotech regulation keeps evolving (1). Step 2: it says regulation must include "socio-economic impacts". So social and economic aspects count (3). Step 3: assumption 2, public participation, and assumption 4, a wider role for the political executive in trade policy, are not mentioned in the passage. So options (a), (c) and (d) fail.
Tip: check each statement against a line in the passage. If you cannot point to a line, the statement is not a valid assumption, however sensible it sounds. India's GM crop approvals are made by the Genetic Engineering Appraisal Committee (GEAC).
Answer as per the official UPSC answer key.
How many integers are there between 1 and 100 which have 4 as a digit but are not divisible by 4?
Answer (c) & explanation
12 such integers exist (c). Step 1: list the numbers from 1 to 100 with a 4 as a digit: 4, 14, 24, 34, 40 to 49 (ten numbers), 54, 64, 74, 84, 94. That is 19 numbers. Step 2: among them, those divisible by 4: 4, 24, 40, 44, 48, 64, 84. That is 7. Step 3: 19 − 7 = 12. Option (b), 11, and option (d), 13, miscount by one. Option (a) misses the 40s.
Tip: count the 40s block separately; it is easy to miss that 44 has two 4s but counts once. A number is divisible by 4 if its last two digits are divisible by 4.
Answer as per the official UPSC answer key.
The average score of a batsman after his 50th innings was 46·4. After 60th innings, his average score increases by 2·6. What was his average score in the last ten innings?
Answer (c) & explanation
His average in the last ten innings was 62 (c). Step 1: total after 50 innings = 50 × 46·4 = 2320. Step 2: the new average after 60 innings = 46·4 + 2·6 = 49. Total = 60 × 49 = 2940. Step 3: runs in the last 10 innings = 2940 − 2320 = 620. Average = 620 ÷ 10 = 62. Option (d), 49, is the new overall average. Options (a) and (b) fail.
Tip: always convert averages to totals before subtracting. Shortcut: the last 10 innings must lift 60 innings by 2·6 each and also match the old average: 46·4 + (60 × 2·6) ÷ 10 = 46·4 + 15·6 = 62.
Answer as per the official UPSC answer key.
Which of the following phrases defines the nature of the ‘Hundi’ generally referred to in the sources of the post-Harsha period ?
Answer (c) & explanation
A hundi was a bill of exchange (c). A hundi was a written order by which a merchant could pay money at a distant place through a banker there. A trader in one town paid money to a shroff (sarraf), who gave him a hundi that could be cashed in another town. This meant traders did not have to carry cash over unsafe roads. It was in use from the early medieval period and through Mughal times, run by networks of shroffs and Marwari bankers. It was not a royal advisory (a), an account diary (b), or a feudal order (d).
Notice the modern echo: the hawala system works in a similar way, but illegally. Hundis were a key part of India's pre-colonial banking system.
Answer as per the official UPSC answer key.
If the RBI decides to adopt an expansionist monetary policy, which of the following would it not do?
- 1. Cut and optimize the Statutory Liquidity Ratio
- 2. Increase the Marginal Standing Facility Rate
- 3. Cut the Bank Rate and Repo Rate
Select the correct answer using the code given below :
Answer (b) & explanation
The RBI would not raise the MSF rate (b). An expansionist monetary policy makes money cheaper and more plentiful to boost growth. Statement 1 fits it: cutting the Statutory Liquidity Ratio frees bank funds that were locked in government securities, so banks can lend more. Statement 3 fits it too: cutting the repo rate and bank rate lowers the cost of borrowing from the RBI. Statement 2 does not fit: raising the Marginal Standing Facility rate makes emergency overnight borrowing dearer, which is a tightening step. So 2 is the only thing it would not do.
Notice the Liquidity Adjustment Facility: since 2022, the Standing Deposit Facility is its floor and the MSF its ceiling. The Monetary Policy Committee has six members.
"would it not do". Mark the tightening step, not the easing ones.
Answer as per the official UPSC answer key.
With reference to the current trends in the cultivation of sugarcane in India, consider the following statements :
- 1. A substantial saving in seed material is made when 'bud chip settlings' are raised in a nursery and transplanted in the main field.
- 2. When direct planting of setts is done, the germination percentage is better with single-budded setts as compared to setts with many buds.
- 3. If bad weather conditions prevail when setts are directly planted, single-budded setts have better survival as compared to large setts.
- 4. Sugarcane can be cultivated using settlings prepared from tissue culture.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Statements 1 and 4 are correct (c). Statement 1 is right: in the bud chip method, only a small chip with one bud is raised in a nursery and then transplanted, saving about 80% of seed cane. Statement 2 is wrong: when planted directly in the field, single-bud setts dry out and germinate poorly; two- or three-bud setts do better. Statement 3 is wrong for the same reason: in bad weather, larger setts survive better. Statement 4 is right: tissue culture produces disease-free settlings for planting.
Notice the Sustainable Sugarcane Initiative (SSI), which combines nursery-raised seedlings, wide spacing and drip irrigation. Uttar Pradesh is the top sugarcane producer; Maharashtra often leads in sugar.
Answer as per the official UPSC answer key.
Let A3BC and DE2F be four-digit numbers where each letter represents a different digit greater than 3. If the sum of the numbers is 15902, then what is the difference between the values of A and D?
Answer (c) & explanation
1. Units: C + F ends in 2 and both digits are at least 4, so C + F = 12, carry 1. Tens: B + 2 + 1 ends in 0, so B = 7, carry 1.
2. Hundreds: 3 + E + 1 ends in 9, so E = 5. Thousands: A + D = 15.
3. Digits left (greater than 3, not 5 or 7): C, F = 4, 8 and A, D = 6, 9. Difference = 3.
Answer as per the official UPSC answer key.
The letters from A to Z are numbered from 1 to 26 respectively. If GHI = 1578 and DEF = 912, then what is ABC equal to?
Answer (d) & explanation
ABC equals 246 (d). Step 1: GHI → DEF → ABC: each letter moves back 3 places at each step. So the code should change by the same amount each step. Step 2: 1578 − 912 = 666. Step 3: ABC = 912 − 666 = 246. Options (a), (b) and (c) do not fit.
Tip: if letter groups shift by a fixed step, their codes often shift by a fixed amount too. Find the gap between two known codes and apply it once more.
Answer as per the official UPSC answer key.