UPSC Prelims PYQs with explanations
Real questions from official papers, mapped to syllabus topics. Attempt each one; the answer and the reason appear instantly.
What is the least four-digit number when divided by 3, 4, 5 and 6 leaves a remainder 2 in each case?
Answer (b) & explanation
The least such number is 1022 (b). Step 1: a number leaving remainder 2 when divided by 3, 4, 5 and 6 has the form LCM × k + 2. LCM(3, 4, 5, 6) = 60. Step 2: the smallest four-digit multiple of 60: 60 × 17 = 1020. Step 3: add 2: 1022. Option (a), 1012, is 60 × 16·8 + 2, not valid. Option (c), 1122 = 60 × 18·67 + 2, fails. Option (d) also fails.
Tip: same remainder for all divisors → number = LCM × k + remainder. Find the LCM, then the first suitable multiple.
Answer as per the official UPSC answer key.
A constitutional government by definition is a
Answer (d) & explanation
A constitutional government is a limited government (d). It works within limits set by a higher law, the constitution. Its powers are defined and restricted, and fundamental rights, separation of powers, judicial review and the rule of law stop it from becoming arbitrary. So it is limited by definition. Option (a) is wrong because government by a legislature need not be limited, as a legislature can also be absolute. Option (b) is wrong because a popular government can still be unlimited and even tyrannical. Option (c) is wrong because multiple parties do not make a government constitutional.
Notice that even the UK, without a written constitution, has constitutional government through conventions. India's Constitution limits Parliament too, through the basic structure doctrine.
Answer as per the official UPSC answer key.
Consider the following activities :
- 1. Spraying pesticides on a crop field
- 2. Inspecting the craters of active volcanoes
- 3. Collecting breath samples from spouting whales for DNA analysis
At the present level of technology, which of the above activities can be successfully carried out by using drones ?
Answer (d) & explanation
Drones can do all three (d). Drones are used to spray pesticides and fertilisers on crops (1), saving time and reducing farmers' exposure to chemicals. India promotes Kisan drones and the Namo Drone Didi scheme (2023), which gives drones to women's SHGs. Drones fly over active volcanoes to inspect craters and sample gases (2), where it is too dangerous for people. In the SnotBot project, drones collect breath samples from spouting whales (3) for DNA, hormone and health studies, without disturbing them. So any option leaving one out is wrong.
Notice India's drone policy: the liberal Drone Rules, 2021, the PLI scheme for drones, and the ban on most imported drones (2022). Drones were used widely in Operation Sindoor (2025).
Answer as per the official UPSC answer key.
With reference to India’s biodiversity, Ceylon frogmouth, Coppersmith barbet, Gray-chinned minivet and White-throated redstart are
Answer (a) & explanation
All four are birds (a). The Ceylon frogmouth is a night bird of the Western Ghats and Sri Lanka, named for its wide, frog-like mouth. The coppersmith barbet is a small green bird named for its call, which sounds like a smith hammering metal. The grey-chinned minivet is a bright songbird of hill forests. The white-throated redstart is a Himalayan bird of high scrub. None of them is a primate (b), reptile (c) or amphibian (d); the frogmouth's name is the only trap.
Notice how UPSC likes species with misleading names. Other bird examples: the Great Indian Bustard (Critically Endangered), the Jerdon's courser, and the Malabar trogon. Notice too the Asian Waterbird Census, held each January.
"frogmouth" pushes you towards amphibians.
Answer as per the official UPSC answer key.
Read the passage
In India, over the last decade or so, labour has been departing agriculture, but is only going to construction and unregistered manufacturing which are not markedly better jobs. Services, where labour tends to be most productive, are not generating the additional jobs the country needs. India will need 24 million or so jobs over the next decade. The new sector, e-commerce, can at best close only half the jobs gap. Only those sectors that drive domestic demand such as health and education can comfortably fill the other half.
Which one of the following is best implied in the passage?
Answer (d) & explanation
The passage best implies that more social-sector spending is vital for large-scale job creation (d). Step 1: it says only health and education "can comfortably fill the other half" of the jobs gap. So spending on these sectors is key to creating jobs. That is (d). Step 2: option (c) says services are reducing unemployment. The passage says they are not generating enough jobs, so (c) is false. Step 3: option (a), stopping rural-urban migration, and option (b), better working conditions in construction, are not the passage's point.
Tip: look for the line that offers a solution; it usually holds the implication. Health and education are labour-intensive, so they create many jobs per rupee spent.
Answer as per the official UPSC answer key.
Two Statements are given followed by two Conclusions :
Statements : All cats are dogs. All cats are black.
Conclusion-I : All dogs are black.
Conclusion-II : Some dogs are not black.
Which of the above Conclusions logically follows/follow from the two given Statements, disregarding commonly known facts?
Answer (c) & explanation
Neither conclusion follows (c). Step 1: "All cats are dogs" puts the cats inside the dogs group. "All cats are black" says the cats are black. Step 2: so we know the cat part of the dogs is black. The other dogs may or may not be black. Step 3: so "all dogs are black" (I) is not certain, and "some dogs are not black" (II) is not certain either. Neither follows. Options (a), (b) and (d) fail.
Tip: draw circles: a small "cats" circle inside "dogs", also inside "black". The rest of "dogs" is unknown. When I and II are opposites, check if they form an either-or pair; here they do not, because "all dogs are black" is only possible, not certain.
I and II are opposites, so one of them must be true. But neither follows by itself, and no option says 'either I or II'.
Answer as per the official UPSC answer key.
Read the passage
Many people understand the connection between solid waste management and health in terms of the consequences of unattended heaps of dry garbage which become home for flies and other vermin. However, there is another aspect that is not well-understood, that is, what happens when unscientific solid waste management combines with poor drainage and dumping of untreated sewage into drains which are meant to carry storm water during rains. The result is choked drains which are full of stagnant water breeding mosquitoes, resulting in the spread of water-borne diseases.
In the context of India, which one of the following statements best reflects the critical message of the passage?
Answer (c) & explanation
The message is that solid waste management must be integrated with drainage and sewerage upkeep (c). Step 1: the passage says disease spreads when poor waste handling "combines with poor drainage" and sewage. So these must be managed together. That is (c). Step 2: option (a), drains not separated for sewage and storm water, is only a detail. Step 3: option (b), local bodies lack money and power, is not the main point. Option (d), drinking water shortage, is not discussed.
Tip: the message usually ties the passage's facts together. Here every fact links waste and drainage. Swachh Bharat Mission (Urban) 2.0 covers both solid waste and used-water management.
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. According to the Constitution of India, a person who is eligible to vote can be made a minister in a State for six months even if he/she is not a member of the Legislature of that State.
- 2. According to the Representation of People Act, 1951, a person convicted of a criminal offence and sentenced to imprisonment for five years is permanently disqualified from contesting an election even after his release from prison.
Which of the statements given above is/are correct?
Answer (d) & explanation
Neither statement is correct (d). Statement 1 is wrong because Article 164(4) lets a non-member be a State minister for six months, but that person must be qualified to become an MLA. That requires a minimum age of 25, not just being a voter, who can be 18. Statement 2 is wrong because, under Section 8(3) of the Representation of the People Act, 1951, a person sentenced to two years or more is disqualified from the date of conviction for the period of the sentence plus six years after release, not permanently.
In Lily Thomas (2013), the Court removed the protection that let sitting MPs and MLAs keep their seats while appealing. Notice the 2025 debate on a lifetime ban for convicted politicians, which the Centre opposed.
"eligible to vote" (age 18) slipped in for "qualified to be a member" (age 25).
Answer as per the official UPSC answer key.
The term 'West Texas Intermediate', sometimes found in news, refers to a grade of
Answer (a) & explanation
WTI is a grade of crude oil (a). West Texas Intermediate is a light, sweet (low-sulphur) crude from US oilfields, priced at the delivery hub of Cushing, Oklahoma. It is one of the three main world price benchmarks, along with Brent (North Sea) and Dubai/Oman (Gulf). In April 2020, WTI futures briefly traded below zero as storage ran out during COVID. It has nothing to do with bullion (b), which means gold and silver bars; rare earth elements (c), which are metals such as neodymium; or uranium (d).
Notice that the Indian crude basket is mostly Dubai-Oman (sour grades) and Brent (sweet). Light, sweet crude is easier and cheaper to refine into petrol and diesel.
Answer as per the official UPSC answer key.
Which one of the following statements best describes the term ‘Social Cost of Carbon’ ?
It is a measure, in monetary value, of the
Answer (a) & explanation
It measures the long-term damage from one tonne of CO₂ (a). The social cost of carbon puts a money value on the harm caused by emitting one more tonne of CO₂ in a given year: lost crops, health damage, floods, heat and lower productivity, added up over time. Governments use it to weigh the costs and benefits of climate policies and regulations. Option (b) describes a country's fossil fuel demand, not damage. Option (c) describes the burden on a climate refugee. Option (d) describes an individual's carbon footprint.
Notice the related ideas of carbon pricing: a carbon tax and emissions trading. India launched its Carbon Credit Trading Scheme in 2023 under the Energy Conservation Act.
Answer as per the official UPSC answer key.
If you have two straight sticks of length 7·5 feet and 3·25 feet, what is the minimum length can you measure?
Answer (b) & explanation
The minimum length you can measure is 0·25 foot (b). Step 1: by adding and subtracting the two sticks, you can measure any multiple of their HCF, and nothing smaller. Step 2: write both in quarter-feet: 7·5 feet = 30 quarters; 3·25 feet = 13 quarters. Step 3: HCF(30, 13) = 1 quarter, which is 0·25 foot. For example, 30 − 2 × 13 = 4 quarters, and 13 − 3 × 4 = 1 quarter. Option (a), 0·05, is too small. Options (c) and (d) are not the minimum.
Tip: the smallest measurable length with two rods is their HCF. Convert decimals to whole units first to find it easily.
Answer as per the official UPSC answer key.
Read the passage
In India, authorities always look to store the maximum amount of water in reservoirs during the monsoon season, which is then used for irrigation and generation of electricity during the summer months. It is an internationally accepted practice that the water level of a reservoir should be kept below a certain level before the onset of monsoon season. This is so that when monsoon rains come, there is space to store the excess rainwater and also so that water can be released in a regulated manner. But the authorities store the maximum amount of water in reservoirs even before the close of the monsoon, only to ensure greater electricity generation and irrigation.
With reference to the above passage, the following assumptions have been made :
- 1. High risks involved in holding maximum water in reservoirs are due to our over-dependence on hydropower projects.
- 2. Storage capacity of dams should not be fully used before or during monsoon season.
- 3. Role of dams in flood control is underestimated in India.
Which of the above assumptions is/are valid?
Answer (d) & explanation
All three assumptions are valid (d). Step 1: the passage says reservoirs are filled early "only to ensure greater electricity generation and irrigation". So the risk comes from over-reliance on hydropower and storage (1). Step 2: it says space must be kept free for monsoon inflows. So dams should not be full before or during the monsoon (2). Step 3: by filling dams early, their flood-control role is ignored (3). So options (a), (b) and (c) fail.
Tip: Kerala's 2018 floods raised this debate: dams full before heavy rain had to release water suddenly. A dam's empty space is itself a flood shield.
Answer as per the official UPSC answer key.
Which one of the following will have minimum change in its value if 5 is added to both numerator and the denominator of the fractions 2/3, 3/4, 4/5 and 5/6?
Answer (d) & explanation
5/6 changes the least (d). Step 1: adding the same number to the top and bottom pulls a fraction towards 1. The fraction already closest to 1 moves the least. Step 2: among 2/3, 3/4, 4/5 and 5/6, the closest to 1 is 5/6. Step 3: check: 5/6 → 10/11, a change of 5/66 (about 0·076). 2/3 → 7/8, a change of 5/24 (about 0·21). So 5/6 changes least. Options (a), (b) and (c) change more.
Tip: the change for a/b with k added is k(b − a) ÷ [b(b + k)]. A bigger b means a smaller change, which favours 5/6.
Answer as per the official UPSC answer key.
In the context of Indian history, the Rakhmabai case of 1884 revolved around
- 1. women’s right to gain education
- 2. age of consent
- 3. restitution of conjugal rights
Select the correct answer using the code given below :
Answer (b) & explanation
The case revolved around age of consent and restitution of conjugal rights (b). Rakhmabai was married at 11 to Dadaji Bhikaji but stayed with her mother and refused to live with him. In 1884, he sued for restitution of conjugal rights (3), and the court finally ordered her to join him or go to jail. She chose jail, and the case ended in a compromise. The public debate it caused helped lead to the Age of Consent Act, 1891 (2), which raised the age of consent from 10 to 12, backed by Behramji Malabari. Statement 1 is wrong because education was not the issue.
Rakhmabai later trained in London and became one of India's first practising women doctors. Notice Anandibai Joshi, often called the first Indian woman to earn a medical degree (1886).
Answer as per the official UPSC answer key.
Consider the following statements :
- 1. The value of Indo-Sri Lanka trade has consistently increased in the last decade.
- 2. "Textile and textile articles" constitute an important item of trade between India and Bangladesh.
- 3. In the last five years, Nepal has been the largest trading partner of India in South Asia.
Which of the statements given above is/are correct ?
Answer (b) & explanation
Only statement 2 is correct (b). Statement 1 is wrong because India–Sri Lanka trade rose and fell with Sri Lanka's troubles, including its 2022 economic crisis; it did not rise "consistently". Statement 2 is right because cotton, yarn and textiles are a major part of India's exports to Bangladesh, which is one of the world's biggest garment exporters and needs raw material. Statement 3 is wrong because Bangladesh, not Nepal, is India's largest trading partner in South Asia.
Notice the India–Sri Lanka Free Trade Agreement (1998, in force 2000) and SAFTA (2004/2006) for South Asia. Nepal is a landlocked country that depends heavily on India for transit and trade, but its total trade is smaller than Bangladesh's.
"consistently" in statement 1. One bad year breaks the claim.
Answer as per the official UPSC answer key.
Siachen Glacier is situated to the
Answer (d) & explanation
Siachen lies north of the Nubra Valley (d). The Siachen Glacier lies in the eastern Karakoram, between the Saltoro Ridge to the west and the Chinese-held Shaksgam area to the east. Its meltwater feeds the Nubra River, which flows south into the Shyok, so the glacier is north of the Nubra valley. Option (a) is wrong: Aksai Chin lies to the east. Option (b) is wrong: Leh lies to the south-east. Option (c) is wrong: Gilgit lies far to the west.
Notice Operation Meghdoot (1984), when India took control of Siachen. It is called the world's highest battlefield. At about 76 km, it is among the longest glaciers outside the polar regions.
Answer as per the official UPSC answer key.
Read the passage
People will invest in education whenever they are granted the economic freedom to fully enjoy its benefits. Again, this is for the obvious reason that the return on education increases as the level of economic freedom rises. When people, thanks to lower tax rates, are allowed to retain most of the higher income that they gain from each incremental level of education, it makes eminent sense to invest in education. On the other hand, when the government decides to tax the higher income of educated individuals at even higher rates, it makes very little sense to invest in educating oneself further. The same incentives apply to parents who decide on whether to invest in their children’s education.
With reference to the above passage, the following assumptions have been made :
- 1. Lower tax rates in a country invariably translate into greater investments in higher education.
- 2. Investment in the education of children ensures their economic freedom.
- 3. Economic freedom has a positive impact on building up human capital.
Which of the above assumptions is/are valid?
Answer (c) & explanation
Only assumption 3 is valid (c). Step 1: the passage says when people are free to keep the returns on their efforts, they invest in education. That builds human capital. So economic freedom helps human capital (3). Step 2: assumption 1 says lower taxes invariably lead to more investment in higher education. "Invariably" (always) overstates. Step 3: assumption 2 reverses the cause. The passage says freedom drives education, not that education ensures freedom. So options (a), (b) and (d) fail.
Tip: watch for reversed cause and effect. "A leads to B" does not mean "B leads to A". Also, "invariably" and "always" need very strong support.
Answer as per the official UPSC answer key.
In adult population of a city, 40% men and 30% women are married. What is the percentage of married adult population if no man marries more than one woman and no woman marries more than one man; and there are no widows and widowers?
Answer (c) & explanation
34 2/7% of adults are married (c). Step 1: each married man has one wife, so married men = married women. So 0·4M = 0·3W, which gives M : W = 3 : 4. Step 2: take M = 300 and W = 400. Married men = 40% of 300 = 120; married women = 30% of 400 = 120. Total married = 240 out of 700. Step 3: 240 ÷ 700 = 24/70 = 34 2/7%. Option (d), 35%, simply averages 40 and 30. Options (a) and (b) fail.
Tip: never average percentages of groups of different sizes. Find the group ratio first, then use real numbers.
Answer as per the official UPSC answer key.
Other than the Fundamental Rights, which of the following parts of the Constitution of India reflect/reflects the principles and provisions of the Universal Declaration of Human Rights (1948)?
- 1. Preamble
- 2. Directive Principles of State Policy
- 3. Fundamental Duties
Select the correct answer using the code given below :
Answer (d) & explanation
All three reflect the UDHR (d). The Universal Declaration of Human Rights was adopted by the UN on 10 December 1948, while India's Constitution was being drafted. The Preamble (1) echoes its ideals of justice, liberty, equality and the dignity of the individual. Many Directive Principles (2) match its social and economic rights, such as the right to work, education, a living wage and humane conditions of work (Articles 39, 41–43). Article 29(1) of the UDHR says everyone has duties to the community, which matches the Fundamental Duties in Part IVA (3).
Notice that 10 December is Human Rights Day. India's Protection of Human Rights Act, 1993 created the NHRC, which follows the Paris Principles.
Answer as per the official UPSC answer key.
“The experiment will employ a trio of spacecraft flying in formation in the shape of an equilateral triangle that has sides one million kilometres long, with lasers shining between the craft.” The experiment in question refers to
Answer (d) & explanation
The experiment is Evolved LISA (d). The Laser Interferometer Space Antenna, in its evolved form (eLISA), plans three spacecraft flying in an equilateral triangle millions of kilometres on a side, with lasers shining between them. Tiny changes in the distance between them will reveal gravitational waves from sources such as merging giant black holes. LISA Pathfinder (c), launched in 2015, was a single craft that only tested the technology. Voyager-2 (a) is exploring interstellar space. New Horizons (b) flew past Pluto in 2015.
The mission, now just called LISA, was approved by the ESA in January 2024, with launch planned around 2035 and arms of about 2.5 million km. Notice its ground-based cousins: LIGO, Virgo, KAGRA and LIGO-India.
Pathfinder was a test of the technology using one spacecraft. The three-spacecraft triangle is the full mission.
Answer as per the official UPSC answer key.