UPSC Prelims PYQs with explanations
Real questions from official papers, mapped to syllabus topics. Attempt each one; the answer and the reason appear instantly.
Consider the following statements in respect of two natural numbers p and q such that p is a prime number and q is a composite number :
- 1. p × q can be an odd number.
- 2. q/p can be a prime number.
- 3. p + q can be a prime number.
Which of the above statements are correct?
Answer (d) & explanation
All three statements are correct (d). Step 1: "can be" needs just one example each. Step 2: statement 1: take p = 3 (prime) and q = 9 (composite). 3 × 9 = 27, odd. Statement 2: p = 2 and q = 6. 6 ÷ 2 = 3, a prime. Step 3: statement 3: p = 2 and q = 9. 2 + 9 = 11, a prime. So options (a), (b) and (c) fail.
Tip: for "can be" statements, look for one working example. Remember 2 is the only even prime, which often helps.
Answer as per the official UPSC answer key.
Among the following crops, which one is the most important anthropogenic source of both methane and nitrous oxide ?
Answer (b) & explanation
Rice is the major source of both gases (b). Flooded paddy fields have no oxygen in the soil, so microbes called methanogens break down organic matter and release methane. The nitrogen fertiliser used on rice adds nitrous oxide, especially when fields are drained and flooded in turns. No other crop does both on that scale. Cotton (a), sugarcane (c) and wheat (d) give off nitrous oxide from fertilisers, but are not grown in flooded fields, so they release little methane.
Notice other farm methane sources: enteric fermentation in cattle, the largest, and manure. India's answers include alternate wetting and drying and Direct Seeded Rice. Nitrous oxide is about 270 times stronger than CO₂ as a warming gas.
Answer as per the official UPSC answer key.
Consider the following freedom fighters :
- 1. Barindra Kumar Ghosh
- 2. Jogesh Chandra Chatterjee
- 3. Rash Behari Bose
Who of the above was/were actively associated with the Ghadar Party ?
Answer (d) & explanation
Only Rash Behari Bose was a Ghadarite (d). Item 3 is right: Rash Behari Bose led the Ghadar plan for an army rising across north India in February 1915; it was betrayed, leading to the Lahore Conspiracy Case, and he escaped to Japan, where he later helped form the Indian National Army. Item 1 is wrong: Barindra Kumar Ghosh, brother of Aurobindo, led the Jugantar group of the Alipore bomb case (1908) in Bengal. Item 2 is wrong: Jogesh Chandra Chatterjee came from the Anushilan Samiti and was a founder of the Hindustan Republican Association (1924).
Notice that the Ghadar Party was founded in 1913 at San Francisco, led by Lala Har Dayal and Sohan Singh Bhakna, mainly among Punjabi migrants in North America.
Answer as per the official UPSC answer key.
Which one of the following statements best reflects the issue with Senkaku Islands, sometimes mentioned in the news ?
Answer (b) & explanation
The Senkaku Islands are disputed by China and Japan (b). The small, uninhabited Senkaku islands, called Diaoyu by China, lie in the East China Sea, north-east of Taiwan. Japan controls them, while China and Taiwan claim them. Option (a) is wrong: they are natural islands; China's artificial islands are in the South China Sea. Option (c) is wrong: there is no permanent US base on them. Option (d) is wrong: the ICJ has never ruled on them, and South-East Asian countries do not claim them.
Notice that the USA says its defence treaty with Japan covers the Senkakus. Do not mix up the seas: the Spratly and Paracel disputes are in the South China Sea, involving China, Vietnam, the Philippines and others.
Answer as per the official UPSC answer key.
Read the passage
The poverty line is quite unsatisfactory when it comes to grasping the extent of poverty in India. It is not only because of its extremely narrow definition of ‘who is poor’ and the debatable methodology used to count the poor, but also because of a more fundamental assumption underlying it. It exclusively relies on the notion of poverty as insufficient income or insufficient purchasing power. One can better categorize it by calling it income poverty. If poverty is ultimately about deprivations affecting human well-being, then income poverty is only one aspect of it. Poverty of a life, in our view, lies not merely in the impoverished state in which the person actually lives, but also in the lack of real opportunity given by social constraints as well as personal circumstances—to choose other types of living. Even the relevance of low incomes, meagre possessions, and other aspects of what are standardly seen as economic poverty relate ultimately to their role in curtailing capabilities, i.e., their role in severely restricting the choices people have to lead variable and valued lives.
What does the author mean by ‘poverty of a life’?
Answer (a) & explanation
'Poverty of a life' means all deprivations, from lack of income and lack of real opportunities (a). Step 1: the passage says poverty of a life lies "not merely in the impoverished state" a person lives in. Step 2: it lies "also in the lack of real opportunity" to choose other ways of living. Both parts appear in (a). Step 3: option (b) covers only the impoverished state. Option (c), missed opportunities, leaves out income. Option (d) adds "permanently", which the passage never says.
Tip: "not merely X but also Y" means the answer must include both X and Y. Options with only one half are traps.
Answer as per the official UPSC answer key.
Aman started from home at 14:30 hours and drove to village, arriving there when the village clock indicated 15:15 hours. After staying for 25 minutes, he drove back by a different route of length 1·25 times the first route at a rate twice as fast reaching home at 16:00 hours. As compared to the clock at home, the village clock is
Answer (d) & explanation
The village clock is 5 minutes fast (d). Step 1: let the outward drive take t minutes. The return route is 1.25 times longer at twice the speed, so it takes 1.25 ÷ 2 = 0.625t. Step 2: by the home clock, he was away 14:30 to 16:00 = 90 minutes. So t + 25 + 0.625t = 90, giving 1.625t = 65 and t = 40. Step 3: he truly reached the village at 14:30 + 40 = 15:10. The village clock showed 15:15, so it is 5 minutes fast. Options (a), (b) and (c) fail.
Tip: use only the reliable clock for time intervals. Then compare the true arrival time with what the other clock showed.
Answer as per the official UPSC answer key.
The sum of three consecutive integers is equal to their product. How many such possibilities are there?
Answer (c) & explanation
There are three such sets (c). Step 1: integers include 0 and negative numbers. Try small sets in a row. Step 2: 1, 2, 3: sum 6, product 6. Works. −1, 0, 1: sum 0, product 0. Works. −3, −2, −1: sum −6, product −6. Works. Step 3: bigger sets fail; for 2, 3, 4 the sum is 9 but the product is 24. The product grows much faster. So there are three. Option (a) counts only positive numbers.
Tip: "integers" means negatives and zero too. UPSC often hides extra answers there.
integers include zero and negatives. If you check only natural numbers, you find just one.
Answer as per the official UPSC answer key.
With reference to Web 3.0, consider the following statements :
- 1. Web 3.0 technology enables people to control their own data.
- 2. In Web 3.0 world, there can be blockchain based social networks.
- 3. Web 3.0 is operated by users collectively rather than a corporation.
Which of the statements given above are correct ?
Answer (d) & explanation
All three statements are correct (d). Web 3.0 is the idea of a decentralised internet built on blockchains. Statement 1 is right: users hold their own data and digital assets in wallets, rather than leaving them with big platforms. Statement 2 is right: applications, including social networks, can run on public blockchains. Statement 3 is right: decisions can be made by users collectively, for example through DAOs (decentralised autonomous organisations), rather than by one company.
Notice the earlier stages: Web 1.0 was read-only static pages; Web 2.0 is today's interactive, platform-run web of social media. Web 3.0 is linked with cryptocurrencies and NFTs. India taxes crypto gains at 30%, with 1% TDS.
Answer as per the official UPSC answer key.
With reference to Convertible Bonds, consider the following statements :
- 1. As there is an option to exchange the bond for equity, Convertible Bonds pay a lower rate of interest.
- 2. The option to convert to equity affords the bondholder a degree of indexation to rising consumer prices.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Both statements are correct (c). A convertible bond pays fixed interest but lets the holder turn it into the company's shares later. Statement 1 is right: investors value that option, so the company can pay a lower coupon than on a plain bond. Statement 2 is right: when consumer prices rise, company revenues and share prices usually rise too, so the right to convert gives some protection, a partial indexation, against inflation. A plain fixed-coupon bond loses real value as prices rise.
Notice the Indian link: Foreign Currency Convertible Bonds (FCCBs) let Indian firms borrow abroad cheaply. Compare inflation-indexed bonds, whose principal itself rises with prices, and perpetual bonds, which never mature.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. Other than those made by humans, nanoparticles do not exist in nature.
- 2. Nanoparticles of some metallic oxides are used in the manufacture of some cosmetics.
- 3. Nanoparticles of some commercial products which enter the environment are unsafe for humans.
Which of the statements given above is/are correct ?
Answer (d) & explanation
Statements 2 and 3 are correct (d). Statement 2 is right: nanoparticles of zinc oxide and titanium dioxide are used in sunscreens, creams and other cosmetics, because they block UV rays without leaving a white layer. Statement 3 is right: some engineered nanoparticles that enter the air, water or soil can be unsafe: their tiny size lets them reach deep into the lungs, cross cell walls and harm tissues. Statement 1 is wrong: nanoparticles occur in nature, in volcanic ash, sea spray, desert dust and smoke from forest fires.
Notice the scale: a nanometre is a billionth of a metre, and nanoparticles are 1–100 nm across. At that size materials behave differently: gold looks red, and silver nanoparticles kill microbes.
Answer as per the official UPSC answer key.
Consider the Question and two Statements given below :
Question : Is Z brother of X?
Statement-1 : X is a brother of Y and Y is a brother of Z.
Statement-2 : X, Y and Z are siblings.
Which one of the following is correct in respect of the Question and the Statements?
Answer (d) & explanation
Even both statements together are not enough (d). Step 1: Statement-1 says X is a brother of Y and Y is a brother of Z. So X and Y are male. Step 2: Statement-2 says all three are siblings, which we already know. Step 3: neither statement tells us Z's gender. Z could be X's brother or sister. So the question cannot be answered. Options (a), (b) and (c) fail.
Tip: in relation questions, "brother of Z" tells you the speaker's gender, not Z's. Always check if the gender of the person asked about is given.
'Y is a brother of Z' tells you Y's gender, not Z's.
Answer as per the official UPSC answer key.
24 men and 12 women can do a piece of work in 30 days. In how many days can 12 men and 24 women do the same piece of work?
Answer (d) & explanation
The data are inadequate (d). Step 1: we are not told how fast a man works compared with a woman. Step 2: if men work faster, the new team (fewer men, more women) is slower, taking more than 30 days. If women work faster, it is quicker. If both work at the same rate, it takes the same 30 days. Step 3: since the answer changes with that one missing fact, we cannot decide. Option (a) assumes equal rates. Option (b) assumes men are faster. Option (c) is vague and not a conclusion.
Tip: before calculating, check whether every rate is given. If one key comparison is missing, "data inadequate" is often right.
(a) assumes a man and a woman work equally fast. The question never says so.
Answer as per the official UPSC answer key.
With reference to the expenditure made by an organisation or a company, which of the following statements is/are correct ?
- 1. Acquiring new technology is capital expenditure.
- 2. Debt financing is considered capital expenditure, while equity financing is considered revenue expenditure.
Select the correct answer using the code given below :
Answer (a) & explanation
Only statement 1 is correct (a). Statement 1 is right: capital expenditure buys assets that last for years, such as machines, buildings and new technology. Revenue expenditure meets day-to-day costs, such as wages, rent and repairs. Statement 2 is wrong: debt and equity are not expenditure at all; they are sources of funds. A firm raises money by borrowing (debt) or selling shares (equity), and then spends it as capital or revenue expenditure. The statement mixes up how money is raised with how it is spent.
Notice the same split in the Union Budget: the revenue account and the capital account. Interest payments are the largest item of the Centre's revenue expenditure; capital spending builds roads, railways and defence assets.
Answer as per the official UPSC answer key.
“If rainforests and tropical forests are the lungs of the Earth, then surely wetlands function as its kidneys.” Which one of the following functions of wetlands best reflects the above statement ?
Answer (d) & explanation
Absorbing heavy metals and excess nutrients is the kidney function (d). Kidneys filter waste out of the blood. Wetlands do the same for water: their aquatic plants, microbes and sediments take up heavy metals and excess nutrients, such as nitrates and phosphates, before the water moves on. That is why they are called the "kidneys of the landscape". Options (a), (b) and (c) are true of wetlands, describing the water cycle, the food web and sediment balance, but they are not "filtering" functions.
Notice that East Kolkata Wetlands, a Ramsar site, treat much of the city's sewage naturally while supporting fisheries. Wetlands also control floods and store carbon. India has rules under the Wetlands (Conservation and Management) Rules, 2017.
Answer as per the official UPSC answer key.
With reference to the “United Nations Credentials Committee”, consider the following statements :
- 1. It is a committee set up by the UN Security Council and works under its supervision.
- 2. It traditionally meets in March, June and September every year.
- 3. It assesses the credentials of all UN members before submitting a report to the General Assembly for approval.
Which of the statements given above is/are correct ?
Answer (a) & explanation
Only statement 3 is correct (a). Statement 3 is right: the Credentials Committee examines the credentials of the representatives of all member states and reports to the General Assembly, which approves the report. Statement 1 is wrong: it is a committee of the General Assembly, not the Security Council. Its nine members are appointed by the Assembly at the start of each regular session on the President's proposal. Statement 2 is wrong: it does not meet in March, June and September; it usually meets once a year, near the end of the session, around November–December.
Notice why it matters: it decides who speaks for a country when rival governments claim the seat. In 2021 it deferred the claims of the Taliban in Afghanistan and the military junta in Myanmar, so the old envoys stayed.
Answer as per the official UPSC answer key.
What is the value of X in the sequence 20, 10, 10, 15, 30, 75, X?
Answer (d) & explanation
X is 225 (d). Step 1: divide each term by the one before it. 10 ÷ 20 = 0.5; 10 ÷ 10 = 1; 15 ÷ 10 = 1.5; 30 ÷ 15 = 2; 75 ÷ 30 = 2.5. Step 2: the multiplier rises by 0.5 each step. The next one is 3. Step 3: X = 75 × 3 = 225. Option (c), 150, uses × 2 again. Options (a) and (b) come from adding instead of multiplying.
Tip: when a sequence falls and then rises sharply, look at the ratios between terms. A steadily growing multiplier is a common UPSC pattern.
Answer as per the official UPSC answer key.
P, Q, R, S, T and U are six members of a family. R is the spouse of Q. U is the mother of T and S is the daughter of U. P's daughter is T and R's son is P. There are two couples in the family. Which one of the following is correct?
No official answer (question dropped) & notes
UPSC dropped this question, so it has no official answer. Step 1: R is married to Q, and R's son is P. So P is the child of the couple Q and R. Step 2: P's daughter is T. So T is the granddaughter of Q (and of R). That matches option (d). Step 3: the genders of Q and R are never given. So "grandfather" (a), "grandmother" (b) and "R is the mother" (c) cannot be fixed. The wording about "two couples" adds more doubt, which is a likely reason UPSC dropped it.
Tip: in family puzzles, mark genders only when the question states them. Practise it, but don't overthink dropped items.
UPSC dropped this question from evaluation, so it has no official answer. It is printed here for practice only.
UPSC dropped this question from evaluation; there is no official answer.
Consider the following statements :
- 1. Between 3:16 p.m. and 3:17 p.m., both hour hand and minute hand coincide.
- 2. Between 4:58 p.m. and 4:59 p.m., both minute hand and second hand coincide.
Which of the above statements is/are correct?
Answer (c) & explanation
Both statements are correct (c). Step 1: after 3 o'clock, the hands meet at (60 ÷ 11) × 3 = 16 4/11 minutes. That is about 3:16:22, between 3:16 and 3:17 (1 is true). Step 2: at 4:58:00, the minute hand is at the 58-minute mark and the second hand at 0. The second hand moves about 59 marks per minute faster. Step 3: it catches up in 58/59 minute, about 59 seconds, near 4:58:59. That is between 4:58 and 4:59 (2 is true). So options (a), (b) and (d) fail.
Tip: the hour and minute hands meet every 65 5/11 minutes. After H o'clock, they meet at (60/11) × H minutes.
Answer as per the official UPSC answer key.
"System of Rice Intensification" of cultivation, in which alternate wetting and drying of rice fields is practised, results in :
- 1. Reduced seed requirement
- 2. Reduced methane production
- 3. Reduced electricity consumption
Select the correct answer using the code given below :
Answer (d) & explanation
All three results follow (d). The System of Rice Intensification (SRI) changes how rice is grown. Item 1 is right: it transplants young single seedlings with wide spacing, so it needs far less seed, often only 5–8 kg per hectare against 40–50 kg normally. Item 2 is right: fields are not kept flooded; alternate wetting and drying lets air into the soil, which cuts the bacteria that produce methane. Item 3 is right: less water to pump means less electricity for tube wells.
Notice that SRI was developed in Madagascar in the 1980s by Henri de Laulanié. Notice related methods: Direct Seeded Rice and System of Wheat Intensification. SRI also often raises yields.
Answer as per the official UPSC answer key.
With reference to the proposals of Cripps Mission, consider the following statements :
- 1. The Constituent Assembly would have members nominated by the Provincial Assemblies as well as the Princely States.
- 2. Any Province, which is not prepared to accept the new Constitution would have the right to sign a separate agreement with Britain regarding its future status.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). Statement 2 is right: under the Cripps proposals (March 1942), any province unwilling to accept the new constitution could stay out and sign a separate agreement with Britain, with the same status as the Indian Union. Statement 1 is wrong because of one word: the constitution-making body would be elected by the provincial assemblies through proportional representation, while only the princely states would nominate their members.
Notice why both sides rejected it. Congress objected to the provincial opt-out, which looked like a seed of Partition, and to nominated princes; Gandhi reportedly called the offer a "post-dated cheque". The League wanted Pakistan clearly accepted. The failure of Cripps led straight to the Quit India call in August 1942.
Elected versus nominated: only the princely states nominated.
Answer as per the official UPSC answer key.