UPSC Prelims PYQs with explanations
Real questions from official papers, mapped to syllabus topics. Attempt each one; the answer and the reason appear instantly.
There are three types of rectangular tiles : 3' × 3', 3' × 7' and 3' × 11'. An area of rectangular shape of dimensions 3' × 100' is to be covered using these tiles without breaking them. If x and y are the maximum and minimum numbers of tiles of various sizes, respectively, that can be used to cover the area exactly, then x – y is
Answer (a) & explanation
x − y is 20 (a). Step 1: every tile is 3' wide, like the strip, so only lengths matter: 3a + 7b + 11c = 100, where a, b, c are the numbers of each tile. Step 2: maximum tiles: use as many short 3' tiles as possible. 100 is not a multiple of 3, but 31 × 3 + 7 = 100. So x = 32 tiles. Step 3: minimum tiles: use as many long 11' tiles as possible. 9 × 11 = 99 leaves 1 (impossible); trying downwards, 8 × 11 + 4 × 3 = 88 + 12 = 100 works with 12 tiles, and no combination with 11 or fewer tiles works. So y = 12. x − y = 20.
Tip: for maximum count, use the smallest pieces; for minimum, the largest. Then adjust to hit the exact total.
Answer as per the official UPSC answer key.
With respect to the Western Hoolock Gibbons, which of the following statements is/are correct ?
- 1. A Sanctuary in North-east India is home to this ape species listed as Endangered in the International Union for Conservation of Nature (IUCN) Red List.
- 2. They have specialized brachiation and can easily swing between trees.
- 3. They possess a strong and heavy build like gorillas, yet are remarkably agile tree climbers.
Select the answer using the code given below :
Answer (b) & explanation
Statements 1 and 2 are correct (b). Statement 1 is right: India's only ape, the western hoolock gibbon, is Endangered on the IUCN Red List and gives its name to the Hollongapar Gibbon Sanctuary in Assam. Statement 2 is right: gibbons move by brachiation, swinging arm over arm through the canopy. Statement 3 is wrong: they are "lesser apes", slim and light, about 6–9 kg, nothing like a heavy gorilla. So options (a), (c) and (d) fail.
Notice their habits: they live in pairs with their young and sing loud duets at dawn. They are found south of the Brahmaputra in the North-East. Rail lines cutting through Hollongapar have raised concern, and canopy bridges were proposed to help them cross.
Answer as per the official UPSC answer key.
Consider the following statements with reference to the Constitution of India :
- 1. There is no Article in the Constitution of India that specifies that the Constitution of India will be officially called the 'Constitution of India'.
- 2. There is no Article in the Constitution of India that specifies that the Indian Independence Act, 1947 and the Government of India Act, 1935 stand repealed.
- 3. There is no Article in the Constitution of India that mentions 26th January, 1950 as the date of the commencement of the Constitution of India.
Which one of the following conclusions based on the above statements is correct ?
Answer (b) & explanation
There is no correct statement (b). The last Articles of the Constitution answer all three. Statement 1 is wrong: Article 393 gives the short title, "the Constitution of India". Statement 2 is wrong: Article 395 repeals the Indian Independence Act, 1947 and the Government of India Act, 1935. Statement 3 is wrong: Article 394 says the remaining provisions come into force on 26 January 1950, the "commencement of this Constitution". So options (a), (c) and (d) fail.
Notice the two dates: some provisions, like citizenship, elections and the provisional Parliament, came into force on 26 November 1949, when the Constitution was adopted. The rest began on 26 January 1950, chosen because the Purna Swaraj pledge was made on that day in 1930.
three negative statements in a row. Turn each one positive in your head: "Is there an Article that…?" Then answer.
Answer as per the official UPSC answer key.
An e-commerce revenue model where the seller has control over pricing but doesn't keep products in stock and instead transfers customer orders and shipment details to a third-party supplier, who then ships the goods directly to the customer, is called :
Answer (a) & explanation
This is the dropshipping model (a). In dropshipping, the online store sets the price and takes the order but keeps no stock. It passes the order to a third-party supplier, who ships straight to the buyer. Option (b) is wrong: in the affiliate model a site earns a commission only for sending buyers to another seller. Option (c) is wrong: a transaction-fee model charges a cut on each sale made on a platform. Option (d) is wrong: an agency seller acts on behalf of the owner, who controls the price.
Notice the trade-off: dropshipping needs little capital, but the seller earns thinner margins and depends on the supplier's quality and speed. India allows 100% FDI only in the marketplace model of e-commerce, not the inventory model.
the affiliate model also holds no stock. The clue is "the seller has control over pricing": an affiliate does not set the price.
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Answer as per the official UPSC answer key.
The top of a table is rectangular and its dimensions are 6′ × 10′. Two rectangular portions of the table top are painted in blue colour; both these portions have dimensions 2.5′ × 8′ and each of them has exactly two sides common with two edges of the table top. If the table is fixed to the ground and the remaining portion of the table top is painted in white, how many different patterns are possible when observed from above?
Answer (b) & explanation
Four patterns are possible (b). Step 1: each blue strip is 2.5′ × 8′. Its 8′ side cannot lie along the 6′ edge, so it lies along a 10′ edge, and it touches two edges, so it sits in a corner. Step 2: two strips on the same 10′ edge would need 8 + 8 = 16′, more than 10′, so they would overlap and merge into one shape. So one strip goes along each 10′ edge. Step 3: each strip can sit at the left or right end of its edge: 2 × 2 = 4 patterns. The table is fixed, so mirror images count as different. Options (a), (c) and (d) miscount.
Tip: in arrangement puzzles, first use the sizes to rule out positions. Then count the free choices and multiply.
Answer as per the official UPSC answer key.
Read the passage
The key source of the battle for clean skies and clear lungs is the fuel we burn—from household Chulhas to the thermal power plants. In most cases, it is biomass or coal. The Supreme Court banned the use of pet coke—the dirtiest of such fuels. The Delhi Government banned the use of coal, which was later extended to the entire National Capital Region. It was also agreed that the thermal power plants would clean up or shut down. Action on this has been patchy to say the least. The lesson from the transition to CNG is that people need alternatives for a ban to be effective. When diesel buses were stopped, CNG supply had to be assured. It also had to be feasible in terms of cost. The Supreme Court agreed that fiscal measures were needed to keep clean fuel cheaper than dirty fuel. Now even as coal is banned, the price of natural gas makes industry uncompetitive.
Which of the following statements is/are correct?
- 1. Thermal power stations in Delhi were required to summarily shut down.
- 2. CNG supplies had to be assured once diesel vehicles were prohibited from plying.
- 3. The Supreme Court banned the use of coal across the National Capital Region.
Select the answer using the code given below.
Answer (c) & explanation
Only statement 2 is correct (c). Step 1: statement 2 matches: "When diesel buses were stopped, CNG supply had to be assured." Correct. Step 2: statement 1 says thermal plants had to summarily shut down. The passage says they would "clean up or shut down", a choice, not an immediate closure. Wrong. Step 3: statement 3 says the Supreme Court banned coal across NCR. The passage says the Delhi Government banned coal, later extended to NCR; the Court banned pet coke. Wrong. Options (a), (b) and (d) fail.
Tip: check who did what. Swapping the actor (Court versus Government) is a common trap in fact-based passages.
Answer as per the official UPSC answer key.
There are two chemicals which do not react with each other. A container contains 10 litres of the chemical A. One litre of this chemical is removed from it and one litre of the chemical B is poured. Then one litre of the mixture is removed from the container and one litre of B is poured. If this process of replacing one litre of the mixture by one litre of B is performed once more, then what is the volume of B that is present in the container approximately (in percentage)?
Answer (b) & explanation
B is about 27% of the container (b). Step 1: each time, 1 litre of the 10-litre mixture is removed, so 9/10 of chemical A stays. Step 2: after three rounds, A left = 10 × (9/10)³ = 10 × 0.729 = 7.29 litres, that is 72.9%. Step 3: the rest is B: 100 − 72.9 = 27.1%, about 27%. Option (a), 25, and the others come from subtracting 10% three times or similar slips.
Tip: for repeated replacement, use: original left = start × (1 − removed/total)ⁿ. Simple subtraction of 10% each time gives the wrong answer.
it is not 3 × 10% = 30%. Later rounds take out some B as well.
Answer as per the official UPSC answer key.
With reference to the climate of Andaman and Nicobar Islands, which of the following statements is/are correct ?
- 1. The climate can be defined as a humid, tropical coastal climate.
- 2. It receives rainfall from both South-west monsoon and North-east monsoon.
- 3. Maximum precipitation is between December and May.
Select the answer using the code given below :
Answer (b) & explanation
Statements 1 and 2 are correct (b). Statement 1 is right: the islands lie close to the equator in the Bay of Bengal, so they are hot and humid all year, a tropical coastal climate. Statement 2 is right: they get rain from both the south-west and north-east monsoons, from about May to December. Statement 3 is wrong: January to April is the driest part of the year, so maximum rain is not between December and May. So options (a), (c) and (d) fail.
Notice the islands' features: Barren Island, India's only active volcano; Saddle Peak, the highest point; and Indira Point, India's southernmost tip. Rich tropical evergreen forests cover them, and cyclones often form nearby.
Answer as per the official UPSC answer key.
Which of the following connectivity projects is/are a part of cooperation between India and the ASEAN member countries ?
- 1. Kaladan Multi-Modal Transit Transport Project
- 2. IMT Trilateral Highway
- 3. Agartala-Akhaura Rail Line
Select the answer using the code given below :
Answer (a) & explanation
Projects 1 and 2 involve ASEAN members (a). Item 1 is right: the Kaladan Multi-Modal project links Kolkata to Sittwe port and on to Mizoram through Myanmar. Item 2 is right: the India–Myanmar–Thailand Trilateral Highway runs from Moreh in Manipur to Mae Sot in Thailand. Myanmar and Thailand are both ASEAN members. Item 3 is wrong: the Agartala–Akhaura rail line links Tripura with Bangladesh, which is not in ASEAN. So options (b), (c) and (d) fail.
Notice the policy: these projects are the backbone of India's Act East Policy (2014), which upgraded the Look East Policy (1991). ASEAN has 11 members since Timor-Leste joined in 2025. Bangladesh links fall under BBIN and BIMSTEC instead.
Answer as per the official UPSC answer key.
With reference to different Committees in India, consider the following details :
| Sl. No. | Committee | Objective | Organization under which it was formed
| 1. | R.N. Malhotra Committee | Comprehensive reforms of Insurance sector in India | Insurance Regulatory and Development Authority of India
| 2. | L.C. Gupta Committee | Preparing a roadmap for the introduction of derivatives trading in India | Securities and Exchange Board of India
| 3. | Urjit R. Patel Committee | Preparing a roadmap for reforming bank lending to the Housing sector | Reserve Bank of India
| 4. | Y.H. Malegam Committee | Preparing a roadmap for reforms in Microfinance sector in India | Reserve Bank of India
In which of the above rows are all the details correctly matched ?
Answer (d) & explanation
Rows 2 and 4 are correct (d). Row 2 is right: the L.C. Gupta Committee (SEBI, 1996-98) prepared the roadmap for derivatives trading. Row 4 is right: the Y.H. Malegam Committee (RBI, 2010-11) reviewed microfinance after the Andhra Pradesh crisis. Row 1 is wrong: the R.N. Malhotra Committee (1993) was set up by the Government of India; IRDA itself was born from its report in 1999. Row 3 is wrong: the Urjit Patel Committee (RBI, 2014) designed the inflation-targeting framework, not housing loans. So options (a), (b) and (c) fail.
Notice the outcome of the Patel Committee: CPI-based inflation targeting of 4% ± 2% and a six-member Monetary Policy Committee (2016).
row 1 has the right subject but the wrong parent. A regulator cannot set up the committee that recommended its own birth.
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Answer as per the official UPSC answer key.
Read the passage
When SARS-CoV-2 was first detected in 2019, it was a truly novel virus for the world. At that time, no one in the world had been exposed to SARS-CoV-2 or had specific immunity against it. In contrast, people across the world have been exposed to HMPV for decades and the virus is well-studied. HMPV and SARS-CoV-2 belong to two very different virus families with fundamentally different characteristics and epidemiology, with strong seasonality seen in HMPV, unlike SARS-CoV-2. Both viruses cause different severity of symptoms, particularly over the long term, and the affected population segments do not fully overlap. In general, HMPV causes milder illness with deaths being very rare and with no long-term post-viral symptoms.
Which of the following conclusions is/are valid?
- 1. Though SARS-CoV-2 and HMPV are similar viruses with somewhat different epidemiology, the former became a pandemic because it was novel and people had not been exposed to it in the past.
- 2. The two viruses have fundamentally different impacts on human populations and should not therefore be dealt with in a similar manner.
Select the answer using the code given below.
Answer (b) & explanation
Only conclusion 2 is valid (b). Step 1: the passage stresses that SARS-CoV-2 and HMPV belong to "two very different virus families" with different seasonality, severity and affected groups. So they affect people differently and should not be handled the same way (2). Step 2: conclusion 1 calls them "similar viruses", which contradicts the passage. Step 3: so options (a), (c) and (d) fail.
Tip: one wrong word ("similar") can sink a long statement. HMPV was first identified in 2001 in the Netherlands; India reported cases in January 2025, and the Health Ministry said there was no unusual rise in illness.
Answer as per the official UPSC answer key.
The ratio of male to female workers in two companies A and B is 13 : 10 and 7 : 5, respectively. If both the companies have the same number of female workers, then what is the ratio of the total number of workers in A to those in B?
Answer (b) & explanation
The ratio of total workers is 23 : 24 (b). Step 1: the female numbers must be equal. In A, males : females = 13 : 10. In B, it is 7 : 5, which equals 14 : 10 (doubling both). Step 2: now both have 10 parts of females. A's total = 13 + 10 = 23 parts. B's total = 14 + 10 = 24 parts. Step 3: so A : B = 23 : 24. Option (a) reverses the order. Options (c) and (d) do not equalise the females first.
Tip: when one group is the same in two ratios, scale the ratios so that group has the same number of parts. Then compare totals directly.
don't add 13 + 10 and 7 + 5 directly. Equalise the common term first.
Answer as per the official UPSC answer key.
Consider the following assertion :
In the Pleistocene period either the Yamuna once flowed into the Indus, or the Sutlej flowed into the Yamuna and one major tributary of either had shifted from the Ganga to the Indus or vice versa.
Which of the following is/are the basis of the above assertion ?
- 1. The Nadi-Sukta of the Rigveda
- 2. The explorations of the Sutlej and the Yamuna by Robert Bruce Foote
- 3. The presence of the same species of dolphins in both the Indus and the Ganga river systems
Select the answer using the code given below :
Answer (d) & explanation
Only the dolphin evidence is a basis (d). Item 3 is right: the Indus and Ganga river dolphins are so close that they were long treated as one species, which only makes sense if the two river systems were once joined. Item 1 is wrong: the Pleistocene ended about 12,000 years ago, long before the Rigveda, so the Nadi-Sukta cannot be evidence for it. Item 2 is wrong: Robert Bruce Foote worked on the stone ages of South India, not these rivers.
Notice the Ganges river dolphin is India's national aquatic animal, and is nearly blind, using echolocation. Project Dolphin (2020) protects it. The Indus dolphin lives mainly in Pakistan, with a small group in the Beas in Punjab.
Answer as per the official UPSC answer key.
Which of the following statements with regard to Black Boxes used in modern aircrafts is/are correct ?
- 1. They carry a beacon emitting red light pulses to facilitate underwater detection.
- 2. They record both the cockpit voice and flight data.
- 3. Their memory units are made using either stainless steel or titanium.
Select the answer using the code given below :
Answer (b) & explanation
Statements 2 and 3 are correct (b). Statement 2 is right: the "black box" is really two orange recorders, the cockpit voice recorder and the flight data recorder. Statement 3 is right: their crash-survivable memory sits in stainless steel or titanium shells. Statement 1 is wrong: under water, the locator beacon sends out ultrasonic pulses, about 37.5 kHz, not red light. So options (a), (c) and (d) fail.
Notice why they are orange: to be easy to spot in wreckage. The beacon works for about 30 to 90 days. Black boxes were key in probing the Air India Ahmedabad crash (June 2025); India's AAIB read its data at a new lab in Delhi. Newer rules call for 25-hour voice recording.
Answer as per the official UPSC answer key.
Which of the following statements in relation to NIRANTAR (National Institute for Research and Application of Natural Resources to Transform, Adapt and Build Resilience), a platform of institutions under the Ministry of Environment, Forest and Climate Change, is/are correct ?
- 1. Ecosystem Survey and Analysis is a vertical under this platform, the lead institute of which is Botanical Survey of India, Kolkata.
- 2. Research and Management of Ecosystem Service is a vertical under this platform, the lead institute of which is Central Zoo Authority, New Delhi.
- 3. Capacity Development Support is a vertical under this platform, the lead institute of which is Indian Institute of Forest Management, Bhopal.
Select the answer using the code given below :
Answer (b) & explanation
Statements 1 and 3 are correct (b). NIRANTAR groups the Environment Ministry's institutes into verticals. Statement 1 is right: Ecosystem Survey and Analysis is led by the Botanical Survey of India, Kolkata, with bodies like the FSI and ZSI. Statement 3 is right: Capacity Development Support is led by the Indian Institute of Forest Management, Bhopal. Statement 2 is wrong: Research and Management of Ecosystem Service is led by ICFRE, Dehradun; the Central Zoo Authority is only a member. So options (a), (c) and (d) fail.
Notice the purpose: pooling institutes avoids duplicate work and links research to climate adaptation and resilience. Other Ministry bodies include the Wildlife Institute of India (Dehradun) and GBPNIHE for the Himalaya.
the Central Zoo Authority does sit in that vertical, but as a member, not the lead.
Answer as per the official UPSC answer key.
Question : If x, y and z are integers, each greater than 1, then is x a prime number?
Statement I : xy2 = 116
Statement II : xz = 261
Answer (a) & explanation
Statement I alone is enough; Statement II alone is not (a). Step 1: Statement I: xy² = 116 = 2² × 29. y is above 1 and y² must divide 116, so y² = 4, y = 2, and x = 29, a prime. So I answers "yes". Step 2: Statement II: xz = 261 = 3² × 29. With x, z above 1, x could be 3, 9, 29 or 87. Some are prime (3, 29), some are not (9, 87). So II fails. Step 3: options (b), (c) and (d) fail.
Tip: break numbers into primes first. A squared variable can only take square factors, which often leaves just one choice.
Answer as per the official UPSC answer key.
X and Y are two runners who run for the same duration of time on the same circular track. They started running at the same time in the same direction with uniform speeds. When X completed 7 rounds, Y did exactly 5. After completing 5 rounds, Y changed his direction and started running in the opposite direction with speed which is double of his earlier speed. On the other hand, X continued to run with the same speed. They stopped running when X completed exactly 21 rounds. How many times did X and Y meet after they had started and before they finally stopped?
Answer (a) & explanation
1. Phase 1, same direction, speeds 7 : 5. X gains 2 rounds, so they meet 2 times. The second meeting is at the start point, when Y turns.
2. Phase 2, opposite directions, speeds 7 and 10. X runs 14 more rounds, which takes 2 units of time. Together they cover 17 × 2 = 34 rounds, so they meet 34 times.
3. The 34th meeting is at the moment they stop, and that one is excluded. Total = 2 + 33 = 35.
read "before they finally stopped". The meeting at the stopping moment does not count.
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Answer as per the official UPSC answer key.
A train has to complete a journey of 800 km. If it meets a minor accident, its speed becomes half of the existing speed. If there is a mechanical defect, the speed becomes one-fourth of the existing speed. On its way, the train meets with a minor accident after 200 km; and 400 km thereafter, it develops a mechanical defect. Had the train developed the mechanical defect after 200 km and met the minor accident 400 km thereafter, it would have taken 4 more hours to reach its destination. What was the original speed of the train in km per hour?
Answer (a) & explanation
The original speed was 200 km/h (a). Step 1: actual journey: 200 km at v; then a minor accident halves speed: 400 km at v/2; then a defect quarters it: 200 km at v/8. Time = 200/v + 800/v + 1600/v = 2600/v. Step 2: other order: 200 km at v; defect: 400 km at v/4; accident halves again: 200 km at v/8. Time = 200/v + 1600/v + 1600/v = 3400/v. Step 3: the difference is 4 hours: 800/v = 4, so v = 200 km/h. Options (b), (c) and (d) fail.
Tip: speed changes multiply: half then a quarter gives one-eighth, in either order. Only the middle stretch differs between the two cases.
the cuts apply to the existing speed. After both events the speed is v/8 in either order. Only the middle 400 km differs.
Answer as per the official UPSC answer key.
Which of the following best explain(s) the rationale for protecting mangrove ecosystems in the context of climate resilience ?
- 1. Mangroves reduce tidal energy and store freshwater, making them ideal sites for paddy cultivation in saline estuarine belts.
- 2. Their salt-sensitive roots filter seawater, making mangroves key to converting coastal land into freshwater aquaculture zones.
- 3. By withstanding tidal surges and offering biomass resources, mangroves function both as natural bio-shields and livelihood bases for rural communities.
Select the answer using the code given below :
Answer (d) & explanation
Only statement 3 explains the rationale (d). Statement 3 is right: by withstanding tidal surges and cyclones, mangroves act as natural bio-shields, and they offer biomass, such as fish, crabs, honey and fuel, for coastal villages. Statement 1 is wrong: mangroves do not store fresh water for paddy. Statement 2 is wrong: they are salt-tolerant, not salt-sensitive. Clearing them for farms or aquaculture ponds is exactly what harms them. So options (a), (b) and (c) fail.
Notice the proof: mangroves cut deaths in the 1999 Odisha super-cyclone and the 2004 tsunami. They also store much blue carbon. India's largest mangrove forest is the Sundarbans; the MISHTI scheme (2023) aims to plant more along the coast.
statement 2 says "salt-sensitive". Mangroves live in salt water because they tolerate it.
Answer as per the official UPSC answer key.
Which of the following statements with regard to the persons with disabilities in India is/are correct ?
- 1. The Rights of Persons with Disabilities Act, an Act passed by the Parliament of India in 2018, mandates reservation in education and employment, places a legal duty on Governments to ensure accessibility and non-discrimination.
- 2. The Sugamya Bharat Abhiyan focuses on achieving universal accessibility for Persons with Disabilities across three key domains — built infrastructure, transport systems and information and communication technology.
- 3. The National Divyangjan Finance and Development Corporation (NDFDC) is a public sector organisation set up by the Ministry of Corporate Affairs as a not-for-profit company to promote entrepreneurship among Persons with Disabilities (PwDs).
Select the answer using the code given below :
Answer (b) & explanation
Only statement 2 is correct (b). Statement 2 is right: the Sugamya Bharat (Accessible India) Abhiyan (2015) works on three areas: built environment, transport and ICT. Statement 1 is wrong: the RPwD Act was passed in 2016, not 2018, though it does mandate reservation and accessibility. Statement 3 is wrong: NDFDC works under the Ministry of Social Justice and Empowerment, not Corporate Affairs. So options (a), (c) and (d) fail.
Notice the RPwD Act's key features: it raised the disability types from 7 to 21, set 4% reservation in government jobs and 5% in higher education for persons with benchmark disabilities, and replaced the 1995 Act. It was passed to fulfil India's duties under the UN Convention (UNCRPD).
true content with one wrong detail (year, ministry). UPSC hides the error in the smallest word.
Answer as per the official UPSC answer key.