UPSC Prelims PYQs with explanations
Real questions from official papers, mapped to syllabus topics. Attempt each one; the answer and the reason appear instantly.
Two Statements S1 and S2 are given below with regard to four numbers P, Q, R and S followed by a Question :
S1 : R is greater than P as well as Q.
S2 : S is not the largest one.
Question : Among four numbers P, Q, R and S, which one is the largest?
Which one of the following is correct in respect of the above Statements and the Question?
Answer (c) & explanation
S1 and S2 together are sufficient, but neither alone (c). Step 1: S1 says R is greater than P and Q. So the largest is either R or S; we know nothing about S. S1 alone is not enough. Step 2: S2 says S is not the largest. Alone, it leaves P, Q or R, so it is not enough. Step 3: together, S1 rules out P and Q, and S2 rules out S. So R is the largest. Options (a), (b) and (d) fail.
Tip: in data sufficiency, test each statement alone first, then together. Mark what each one rules out. If the two together leave exactly one answer, choose "together sufficient".
Answer as per the official UPSC answer key.
How many different sums can be formed with the denominations ₹ 50, ₹ 100, ₹ 200, ₹ 500 and ₹ 2,000 taking at least three denominations at a time?
Answer (a) & explanation
16 different sums can be formed (a). Step 1: we take at least three notes, each a different denomination. Choose 3 out of 5: 5C3 = 10 ways. Choose 4: 5C4 = 5 ways. Choose all 5: 1 way. Step 2: total = 10 + 5 + 1 = 16. Step 3: no two choices give the same total, because these notes (50, 100, 200, 500, 2000) never add up to each other's sums. So all 16 sums are different. Options (b), (c) and (d) miscount.
Tip: total selections of 5 items = 2⁵ = 32. Minus those with 0, 1 or 2 items (1 + 5 + 10 = 16) gives 16. Both routes agree.
Answer as per the official UPSC answer key.
One common agreement between Gandhism and Marxism is
Answer (a) & explanation
Both aim at a stateless society (a). Marx expected that after a revolution and a period of the dictatorship of the proletariat, a classless society would emerge and the state would wither away. Gandhi wanted an "enlightened anarchy" of self-governing villages (Gram Swaraj), where people would rule themselves and the state would not need force. Option (b) is wrong because Gandhi rejected class struggle and violence. Option (c) is wrong because Gandhi preferred trusteeship, where the rich hold wealth for society, instead of abolishing private property. Option (d) is wrong because Gandhi rejected economic determinism, putting moral and spiritual values first.
Notice the Gandhian ideas in the Constitution: village panchayats (Article 40), cottage industries (43) and prohibition (47).
Answer as per the official UPSC answer key.
Which of the following are the reasons/factors for exposure to benzene pollution ?
- 1. Automobile exhaust
- 2. Tobacco smoke
- 3. Wood burning
- 4. Using varnished wooden furniture
- 5. Using products made of polyurethane
Select the correct answer using the code given below :
Answer (a) & explanation
Factors 1, 2 and 3 are correct in UPSC's key (a). Benzene is released when carbon-rich material burns incompletely. Major sources are vehicle exhaust (1), as benzene is in petrol and is formed during burning; tobacco smoke (2), the main source for smokers; and wood burning (3), including stoves and forest fires. Benzene is a known cause of leukaemia and other blood cancers. UPSC's key leaves out varnished furniture (4) and polyurethane products (5), which give off other volatile organic compounds such as formaldehyde.
Notice India's limits: BS-VI fuel (from 2020) limits benzene in petrol to 1%, and the National Ambient Air Quality Standards set a yearly limit of 5 µg/m³. Petrol pumps use vapour recovery systems.
Answer as per the official UPSC answer key.
What is the use of biochar in farming ?
- 1. Biochar can be used as a part of the growing medium in vertical farming.
- 2. When biochar is a part of the growing medium, it promotes the growth of nitrogen-fixing microorganisms.
- 3. When biochar is a part of the growing medium, it enables the growing medium to retain water for longer time.
Which of the statements given above is/are correct ?
Answer (d) & explanation
All three statements are correct (d). Biochar is a charcoal made by heating crop waste or wood with little oxygen (pyrolysis). Statement 1 is right: biochar can be mixed into the soil-less growing media used in vertical farming, along with cocopeat and others. Statement 2 is right: its porous body gives a home to useful microbes, including nitrogen-fixing bacteria. Statement 3 is right: those same pores hold water and nutrients, so the medium stays moist for longer.
Notice its climate benefit: biochar locks carbon in the soil for hundreds of years, a form of carbon sequestration. Turning crop stubble into biochar is also proposed as an alternative to stubble burning in Punjab and Haryana.
Answer as per the official UPSC answer key.
How many zeroes are there at the end of the following product? 1 × 5 × 10 × 15 × 20 × 25 × 30 × 35 × 40 × 45 × 50 × 55 × 60
Answer (a) & explanation
The product ends in 10 zeros (a). Step 1: each zero needs one 2 and one 5. Step 2: count the 5s. The 12 numbers from 5 to 60 each give one 5. 25 and 50 give one extra each. Total = 14 fives. Step 3: count the 2s. Only the even numbers give 2s: 10 (one), 20 (two), 30 (one), 40 (three), 50 (one), 60 (two). Total = 10 twos. Zeros = the smaller count = 10. Option (c), 14, counts only the 5s. Options (b) and (d) are also wrong.
Tip: usually 2s are plentiful and 5s are scarce. Here most numbers are odd multiples of 5, so the 2s run out first. Always count both.
here the 2s run out first. Counting only the 5s gives 14, which is a trap option.
Answer as per the official UPSC answer key.
The average age of a teacher and three students is 20 years. If all the three students are of same age and the difference between the age of the teacher and each student is 20 years, then what is the age of the teacher?
Answer (c) & explanation
The teacher is 35 years old (c). Step 1: the average of 4 people is 20, so their total = 80 years. Step 2: let each student be s years. The teacher is s + 20. So 3s + (s + 20) = 80, which gives 4s = 60 and s = 15. Step 3: teacher = 15 + 20 = 35 years. Check: 15 + 15 + 15 + 35 = 80. Option (d), 45, and options (a) and (b) fail this check.
Tip: turn the average into a total first (average × number). Then use one letter for the unknown and build a simple equation. Always check by adding back.
Answer as per the official UPSC answer key.
A person X can complete 20% of work in 8 days and another person Y can complete 25% of the same work in 6 days. If they work together, in how many days will 40% of the work be completed?
Answer (a) & explanation
40% of the work takes 6 days (a). Step 1: X does 20% in 8 days, so the full job takes 40 days. Y does 25% in 6 days, so the full job takes 24 days. Step 2: together, per day: 1/40 + 1/24 = 3/120 + 5/120 = 8/120 = 1/15. So together they finish in 15 days. Step 3: 40% of the job takes 0·4 × 15 = 6 days. Option (b), 8, and the others fail.
Tip: convert each person's partial work into full-job time. Then add daily rates (1/days), not days. Using LCM units (here 120 units of work) also makes it quick.
Answer as per the official UPSC answer key.
The Gandhi-Irwin Pact included which of the following ?
- 1. Invitation to Congress to participate in the Round Table Conference
- 2. Withdrawal of Ordinances promulgated in connection with the Civil Disobedience Movement
- 3. Acceptance of Gandhiji’s suggestion for enquiry into police excesses
- 4. Release of only those prisoners who were not charged with violence
Select the correct answer using the code given below :
No official answer (question dropped) & notes
UPSC dropped this question from evaluation, so no answer was scored. Under the Gandhi–Irwin Pact (5 March 1931), the Congress agreed to suspend Civil Disobedience and attend the Second Round Table Conference (1). The government agreed to withdraw the ordinances issued against the movement (2) and to release political prisoners not charged with violence (4). It also allowed people near the coast to make salt for their own use and gave back confiscated land not yet sold. Statement 3 was rejected: Irwin refused Gandhi's demand for an enquiry into police excesses. So options with 1, 2 and 4 come closest, but the wording "only those prisoners" made the question unclear.
Notice the Karachi session (1931), which approved the pact and passed the Fundamental Rights resolution. Bhagat Singh was hanged that same month.
UPSC did not evaluate this question, so no official answer exists. Use it for practice only.
UPSC dropped this question from evaluation; there is no official answer.
Consider the following statements :
- 1. In terms of short-term credit delivery to the agriculture sector, District Central Cooperative Banks (DCCBs) deliver more credit in comparison to Scheduled Commercial Banks and Regional Rural Banks.
- 2. One of the most important functions of DCCBs is to provide funds to the Primary Agricultural Credit Societies.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). Statement 1 is wrong because Scheduled Commercial Banks give the largest share of short-term crop loans in India, well ahead of cooperative banks and Regional Rural Banks. Statement 2 is right. India's short-term cooperative credit system has three tiers: the State Cooperative Bank at the top, the District Central Cooperative Banks in the middle, and the Primary Agricultural Credit Societies in villages. A key job of the DCCBs is to fund the PACS, which lend straight to farmers.
Notice NABARD, which refinances these banks. The Ministry of Cooperation (2021) is now computerising PACS. Since 2020, cooperative banks also come under fuller RBI regulation after amendments to the Banking Regulation Act.
Answer as per the official UPSC answer key.
What are the advantages of fertigation in agriculture ?
- 1. Controlling the alkalinity of irrigation water is possible.
- 2. Efficient application of Rock Phosphate and all other phosphatic fertilizers is possible.
- 3. Increased availability of nutrients to plants is possible.
- 4. Reduction in the leaching of chemical nutrients is possible.
Select the correct answer using the code given below :
Answer (c) & explanation
Statements 1, 3 and 4 are correct (c). Fertigation feeds dissolved fertiliser through drip or sprinkler lines. Statement 1 is right: acids can be added to the water to correct its alkalinity, which also keeps drippers clean. Statement 3 is right: nutrients reach the roots in small, timely doses, so plants take up more. Statement 4 is right: because less fertiliser is applied at once, less is leached below the roots into groundwater. Statement 2 is wrong: rock phosphate does not dissolve in water, so it cannot be applied this way, and nor can all phosphatic fertilisers.
Notice that fertigation pairs naturally with micro-irrigation, promoted under Per Drop More Crop (PMKSY). Fertigation is common in Israel.
the word "all" in statement 2. Fertigation needs fully water-soluble fertilisers.
Answer as per the official UPSC answer key.
Consider the following data :
| Average marks in English | Average marks in Hindi | |
|---|---|---|
| Girls | 9 | 8 |
| Boys | 8 | 7 |
| Overall average marks | 8·8 | x |
What is the value of x in the above table?
Answer (a) & explanation
x is 7·8 (a). Step 1: in English, girls average 9 and boys 8. The class average of 8·8 is much nearer 9. So most of the class are girls. Step 2: try 10 students: 8 girls and 2 boys. (8 × 9 + 2 × 8) ÷ 10 = 88 ÷ 10 = 8·8. It fits. So the ratio is 4 : 1. Step 3: Hindi, same class: (8 × 8 + 2 × 7) ÷ 10 = 78 ÷ 10 = 7·8. Options (b), (c) and (d) do not fit this ratio.
Tip: a weighted average sits closer to the bigger group. Use the alligation idea: distances 0·2 and 0·8 give the ratio 4 : 1.
Answer as per the official UPSC answer key.
What is the largest number among the following?
Answer (c) & explanation
(1/3)⁻⁴ is the largest (c). Step 1: a negative power flips the fraction: (1/a)⁻ⁿ = aⁿ. Step 2: so (1/2)⁻⁶ = 2⁶ = 64; (1/4)⁻³ = 4³ = 64; (1/3)⁻⁴ = 3⁴ = 81; (1/6)⁻² = 6² = 36. Step 3: the largest is 81, option (c). Options (a) and (b) tie at 64. Option (d) is the smallest.
Tip: remember x⁻ⁿ = 1/xⁿ. Flipping first turns the question into simple powers. Know powers of 2 up to 2¹⁰ = 1024 and of 3 up to 3⁶ = 729.
Answer as per the official UPSC answer key.
Rajya Sabha has equal powers with Lok Sabha in
Answer (b) & explanation
The Rajya Sabha is equal in amending the Constitution (b). Under Article 368, an amendment Bill must pass each House separately by a special majority: a majority of total membership and two-thirds of those present and voting. There is no joint sitting to break a deadlock, so the Rajya Sabha is fully equal. Option (a) is wrong because creating a new All India Service begins with a Rajya Sabha resolution under Article 312, which is a special power of the Rajya Sabha, not an equal one. Options (c) and (d) are wrong because no-confidence motions and cut motions belong only to the Lok Sabha, to which the government is responsible.
Notice the Rajya Sabha's other special power: Article 249, letting Parliament make laws on State List subjects.
(a) is a power of the Rajya Sabha, but it is exclusive, not "equal".
Answer as per the official UPSC answer key.
With the present state of development, Artificial Intelligence can effectively do which of the following ?
- 1. Bring down electricity consumption in industrial units
- 2. Create meaningful short stories and songs
- 3. Disease diagnosis
- 4. Text-to-Speech Conversion
- 5. Wireless transmission of electrical energy
Select the correct answer using the code given below :
Answer (b) & explanation
AI could do tasks 1, 3 and 4 in UPSC's 2020 key (b). By 2020, AI was already proven at cutting electricity use in industry (1), for example Google's DeepMind cutting data centre cooling energy by about 40%. It could help diagnose diseases (3) from X-rays, scans and eye images. It was widely used for text-to-speech (4). Statement 5 is wrong because wireless power transfer is a matter of physics, not AI. UPSC's key also left out writing meaningful stories and songs (2).
Keep the year in mind: since ChatGPT (late 2022), generative AI can clearly write stories and songs. Notice India's moves: the IndiaAI Mission (2024, ₹10,372 crore), the AI Impact Summit in New Delhi (February 2026) and AI governance guidelines (2025).
This answer reflects 2020. A question set today might count creative writing.
Answer as per the official UPSC answer key.
With reference to the Indian economy, consider the following statements :
- 1. 'Commercial Paper' is a short-term unsecured promissory note.
- 2. 'Certificate of Deposit' is a long-term instrument issued by the Reserve Bank of India to a corporation.
- 3. 'Call Money' is a short-term finance used for interbank transactions.
- 4. 'Zero-Coupon Bonds' are the interest bearing short-term bonds issued by the Scheduled Commercial Banks to corporations.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Statements 1 and 3 are correct (c). Statement 1 is right: Commercial Paper is a short-term unsecured promissory note issued by companies, usually for 7 days to a year. Statement 3 is right: call money is very short-term lending between banks, from overnight (call) up to 14 days (notice money). Statement 2 is wrong: a Certificate of Deposit is a short-term deposit receipt issued by banks and some financial institutions, not by the RBI. Statement 4 is wrong: a zero-coupon bond pays no interest; it is sold at a discount and redeemed at face value.
Notice that these are all money market instruments, along with Treasury Bills and repos. The Treasury Bill itself is a zero-coupon instrument.
a "zero-coupon" bond described as "interest bearing". The name itself says no coupon.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. The Constitution of India defines its 'basic structure' in terms of federalism, secularism, fundamental rights and democracy.
- 2. The Constitution of India provides for 'judicial review' to safeguard the citizens' liberties and to preserve the ideals on which the Constitution is based.
Which of the statements given above is/are correct?
Answer (d) & explanation
Neither statement is correct (d). Statement 1 is wrong because the basic structure is not defined anywhere in the Constitution. It comes from court judgments, mainly Kesavananda Bharati (1973). Later cases added features such as federalism, secularism, democracy and judicial review. Statement 2 is wrong in UPSC's view because the phrase "judicial review" does not appear in the text. The power comes from Articles 13, 32, 136 and 226, and the courts treat it as part of the basic structure, but the Constitution does not "provide for" it in those words.
Notice the important basic structure cases: Indira Gandhi v. Raj Narain (1975), Minerva Mills (1980) and S.R. Bommai (1994), which added secularism and federalism.
the power of judicial review exists, so statement 2 feels right. UPSC was testing whether the Constitution "provides for" it in those words.
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Answer as per the official UPSC answer key.
Two Statements S1 and S2 are given below followed by a Question :
S1 : n is a prime number.
S2 : n leaves a remainder of 1 when divided by 4.
Question : If n is a unique natural number between 10 and 20, then what is n?
Which one of the following is correct in respect of the above Statements and the Question?
Answer (d) & explanation
Even together, S1 and S2 are not sufficient (d). Step 1: S1: n is prime and between 10 and 20. That leaves 11, 13, 17 and 19. Not unique. Step 2: S2: n leaves remainder 1 when divided by 4. Between 10 and 20 that gives 13 and 17. Not unique either. Step 3: together, both 13 and 17 are prime and leave remainder 1 (13 = 12 + 1, 17 = 16 + 1). Still two values. So the data are not enough. Options (a), (b) and (c) fail.
Tip: "unique" means exactly one answer. If two values still survive, the statements are insufficient. Listing the candidates is the safest method here.
Answer as per the official UPSC answer key.
Read the passage
Bank credit to the industrial sector has started shrinking. Its decline has been a serious concern as credit growth is essential to revive investment. The problem’s origins lie in the incomplete reforms of the last 25 years. An institutional change that should have followed the 1991 reforms should have been setting up of a resolution corporation for banks. In a market economy with booms and busts, banks should be allowed to be set up and to fail. Today, we cannot shut down banks because there is no proper system to shut them down. Weak loss-making banks continue to need more capital.
Which one of the following is the most logical and rational inference that can be made from the above passage?
Answer (c) & explanation
The inference is that India lacks a system to deal with failed banks (c). Step 1: the passage says "we cannot shut down banks because there is no proper system to shut them down". So India lacks an institutional way to handle bank failure. That is (c). Step 2: options (a) and (b) say banks cannot help growth and that 1991 reforms failed. Both are too sweeping. Step 3: option (d), foreign investment as an alternative, is not discussed.
Tip: when a passage states a problem in one clear line, the inference usually restates it. Note: the Insolvency and Bankruptcy Code, 2016 covers firms; banks still lack a separate resolution law. But answer only from the passage.
Answer as per the official UPSC answer key.
In the context of India, which one of the following is the characteristic appropriate for bureaucracy?
Answer (d) & explanation
Bureaucracy is an agency for implementing public policy (d). In India, elected ministers make policy, and the permanent civil service carries it out. The bureaucracy is meant to be neutral, permanent and selected on merit. It gives continuity when governments change. Options (a), (b) and (c) describe possible effects of a good bureaucracy, such as strengthening democracy or federalism, or helping growth and stability, but not its defining role.
Sardar Patel called the All India Services the "steel frame" of India. Notice Articles 308–323 on services and the UPSC. Reforms such as Mission Karmayogi (2020) for training and lateral entry of experts, which was paused in 2024, are frequent debates.
Answer as per the official UPSC answer key.