UPSC Prelims PYQs with explanations
Real questions from official papers, mapped to syllabus topics. Attempt each one; the answer and the reason appear instantly.
Three persons start walking together and their steps measure 40 cm, 42 cm and 45 cm respectively. What is the minimum distance each should walk so that each can cover the same distance in complete steps?
Answer (a) & explanation
25 m 20 cm is correct (a). Step 1: each person must cover the same distance in whole steps, so the distance must be a multiple of 40, 42 and 45. The minimum is their LCM. Step 2: break into primes: 40 = 2³ × 5; 42 = 2 × 3 × 7; 45 = 3² × 5. LCM = 2³ × 3² × 5 × 7 = 2,520 cm. Step 3: 2,520 cm = 25 m 20 cm. The other options are 2, 3 and 4 times this, so they are not the minimum. So (b), (c) and (d) fail.
Tip: 'minimum common distance' or 'first time together' means LCM. Take the highest power of each prime factor.
Answer as per the official UPSC answer key.
Read the passage
In spring, polar bear mothers emerge from dens with three month old cubs. The mother bear has fasted for as long as eight months but that does not stop the young from demanding full access to her remaining reserves. If there are triplets, the most persistent stands to gain an extra meal and it may have the meal at the expense of others. The smallest of the litter forfeits many meals to stronger siblings. Females are protective of their cubs but tend to ignore family rivalry over food. In 21 years of photographing polar bears, I’ve only once seen the smallest of triplets survive till autumn.
With reference to the passage, the following assumptions have been made :
- 1. Polar bears fast as long as eight months due to non-availability of prey.
- 2. Polar bears always give birth to triplets.
Which of the assumptions given above is/are valid ?
Answer (d) & explanation
Neither assumption is valid (d). Step 1: assumption 1 gives a reason for the eight-month fast: no prey. The passage says the mother 'has fasted for as long as eight months' but never gives the cause. So 1 is not valid. Step 2: assumption 2 says polar bears always give birth to triplets. The passage says 'If there are triplets', which shows that litter sizes vary. So 2 is not valid. Step 3: options (a), (b) and (c) fail.
Tip: 'if' signals a possibility, not a rule, so 'always' fails. And a fact stated without its cause cannot support an assumption about the cause.
Answer as per the official UPSC answer key.
The Himalayan Range is very rich in species diversity. Which one among the following is the most appropriate reason for this phenomenon ?
Answer (b) & explanation
The answer is (b). The Himalaya is rich in species because it is a meeting point of different biogeographic realms: the Palaearctic (Eurasian) to the north, the Indo-Malayan (Oriental) to the east and south, and elements from the Ethiopian (African) realm in the west. Its great altitudinal range, from tropical foothills to alpine zones, packs many habitats into a short distance. Option (a) is wrong because rainfall varies widely, from wet east to dry west and the cold desert of Ladakh. Option (c) is wrong because invasive species, such as Lantana, have spread there. Option (d) is wrong because human pressure is heavy.
Notice the classification: India's Biogeographic Zones (Rodgers and Panwar) number 10, and the Himalaya and Trans-Himalaya are two of them. The Himalaya is part of a global biodiversity hotspot. The eastern Himalaya is richer than the western. Trap: rainfall is not the main reason.
Answer as per the official UPSC answer key.
With reference to micro-irrigation, which of the following statements is/are correct ?
- 1. Fertilizer/nutrient loss can be reduced.
- 2. It is the only means of irrigation in dry land farming.
- 3. In some areas of farming, receding of ground water table can be checked.
Select the correct answer using the codes given below :
Answer (c) & explanation
Statements 1 and 3 are correct (c). Micro-irrigation, through drip and sprinklers, puts water right at the roots; fertiliser dissolved in it (fertigation) is used better, so nutrient loss is reduced (1). Because far less water is used, less groundwater is pumped, which can check the falling water table (3). Statement 2 is wrong: it is not the only means of irrigating dry land; tanks, wells, check dams and watershed works are also used. So (a), (b) and (d) fail.
Notice the scheme: 'Per Drop More Crop', part of PM Krishi Sinchayee Yojana (2015), funds drip and sprinklers, and the Micro Irrigation Fund with NABARD supports states. Trap: 'only' makes statement 2 an overstatement.
Answer as per the official UPSC answer key.
Regarding the Indus Valley Civilization, consider the following statements :
- 1. It was predominantly a secular civilization and the religious element, though present, did not dominate the scene.
- 2. During this period, cotton was used for manufacturing textiles in India.
Which of the statements given above is/are correct ?
Answer (c) & explanation
Both statements are correct per UPSC's key (c), though statement 1 is an interpretation. Harappan cities have no clear temples or palaces of priest-kings; seals, the 'Proto-Shiva', mother goddess figurines and fire altars show that religion was present but did not dominate public life, so many scholars call it largely secular (1). Harappans were among the first in the world to grow and weave cotton; a cotton fragment was found at Mohenjo-daro, and Greeks later called cotton 'sindon' (2). So (a), (b) and (d) fail.
Notice the caution: the script is undeciphered, so views on religion remain tentative. Other facts: the Great Bath, granaries, and planned drains. Dholavira became a World Heritage Site in 2021. Trap: absence of temples is not absence of religion.
Answer as per the official UPSC answer key.
Read the passage
Ecosystems provide people with a variety of goods and services; food, clean water, clean air, flood control, soil stabilization, pollination, climate regulation, spiritual fulfilment and aesthetic enjoyment, to name just a few. Most of these benefits either are irreplaceable or the technology necessary to replace them is prohibitively expensive. For example, potable fresh water can be provided by desalinating sea-water, but only at great cost.
The rapidly expanding human population has greatly modified the Earth’s ecosystems to meet their increased requirements of some of the goods and services, particularly food, fresh water, timber, fibre and fuel. These modifications have contributed substantially to human well being and economic development. The benefits have not been equally distributed. Some people have actually been harmed by these changes. Moreover, short-term increases in some ecosystem goods and services have come at the cost of the long-term degradation of others. For example, efforts to increase the production of food and fibre have decreased the ability of some ecosystems to provide clean water, regulate flooding and support biodiversity.
With reference to the passage, consider the following statements :
- 1. It is imperative to modify the Earth’s ecosystems for the well being of mankind.
- 2. Technology can never replace all the goods and services provided by ecosystems.
Which of the statements given above is/are correct ?
Answer (d) & explanation
Neither statement is correct (d). Step 1: statement 1 says it is imperative to modify ecosystems. The passage only records that modifications happened and helped development; it never says they are necessary, and it stresses the harm. So 1 is wrong. Step 2: statement 2 says technology can never replace ecosystem services. The passage says most are irreplaceable or the technology is 'prohibitively expensive', and gives desalination as a costly but working replacement. So 'never' overstates it. Step 3: options (a), (b) and (c) fail.
Tip: strong words like 'imperative', 'never' and 'always' are red flags. Check whether the passage is that absolute.
Answer as per the official UPSC answer key.
The houses of A and B face each other on a road going north-south, A's being on the western side. A comes out of his house, turns left, travels 5 km, turns right, travels 5 km to the front of D's house. B does exactly the same and reaches the front of C's house. In this context, which one of the following statements is correct?
Answer (c) & explanation
Less than 20 km apart is correct (c). Step 1: A lives on the west side, so he faces east when he comes out. Turning left means going north 5 km; turning right then means going east 5 km. So D's house is 5 km north and 5 km east of A. Step 2: B lives on the east side and faces west. Left means south 5 km; right then means west 5 km. So C's house is 5 km south and 5 km west of B. Step 3: C and D are about 10 km apart north–south and roughly 10 km apart east–west, so the straight distance is about 14 km, well under 20 km. (a) and (b) cannot be fixed from the data. So (a), (b) and (d) fail.
Tip: draw it. Mark which way each person faces first; 'left' depends on that.
Answer as per the official UPSC answer key.
Satellites used for telecommunication relay are kept in a geostationary orbit. A satellite is said to be in such an orbit when :
- 1. The orbit is geosynchronous.
- 2. The orbit is circular.
- 3. The orbit lies in the plane of the Earth’s equator.
- 4. The orbit is at an altitude of 22,236 km.
Select the correct answer using the codes given below :
Answer (a) & explanation
Statements 1, 2 and 3 are correct (a). A geostationary orbit is a special geosynchronous orbit: the satellite completes one revolution in one sidereal day (about 23 h 56 min) (1). It must be circular (2) and lie in the plane of the equator (3), moving west to east, so it appears fixed above one spot. Statement 4 is wrong: the altitude is about 35,786 km, which is 22,236 miles, not 22,236 km. So options (b), (c) and (d) fail.
Notice the difference: every geostationary orbit is geosynchronous, but a geosynchronous orbit can be inclined or elliptical and then traces a figure-of-eight. India's GSAT and INSAT satellites use GEO, launched on the GSLV and LVM3. The NavIC system uses both geostationary and inclined geosynchronous satellites. Trap: the number 22,236 is right only in miles.
Answer as per the official UPSC answer key.
With what purpose is the Government of India promoting the concept of “Mega Food Parks” ?
- 1. To provide good infrastructure facilities for the food processing industry.
- 2. To increase the processing of perishable items and reduce wastage.
- 3. To provide emerging and eco-friendly food processing technologies to entrepreneurs.
Select the correct answer using the codes given below :
Answer (b) & explanation
Statements 1 and 2 are correct as per UPSC's key (b). The Mega Food Park scheme (Ministry of Food Processing Industries, 2008) built shared infrastructure such as cold chains, warehouses and processing centres on a cluster model (1), so that more perishables are processed near farms and less is wasted (2). Statement 3 is not a stated aim: the scheme gives infrastructure, not technology supply to entrepreneurs. So (a), (c) and (d) fail; the line is fine, so treat the key as convention.
Notice the later history: Mega Food Parks became part of PM Kisan SAMPADA Yojana (2017), and no new parks have been sanctioned since 2020–21; focus moved to PLI for food processing and the PMFME scheme for micro units.
Answer as per the official UPSC answer key.
With reference to the period of Indian freedom struggle, which of the following was/were recommended by the Nehru report ?
- 1. Complete Independence for India.
- 2. Joint electorates for reservation of seats for minorities.
- 3. Provision of fundamental rights for the people of India in the Constitution.
Select the correct answer using the codes given below :
Answer (b) & explanation
Statements 2 and 3 are correct (b). The Nehru Report (1928), drafted by a committee under Motilal Nehru in reply to the all-white Simon Commission, proposed joint electorates with reserved seats for minorities (2) and a list of fundamental rights (3). Statement 1 is wrong: it asked for dominion status, not complete independence, which upset younger leaders like Jawaharlal Nehru and Subhas Bose. So (a), (c) and (d) fail.
Notice what followed: Jinnah's Fourteen Points (1929) rejected the report, and the Lahore Congress (December 1929) adopted Purna Swaraj, celebrated on 26 January 1930. The report also proposed linguistic provinces and universal adult franchise. Trap: 'complete independence' came a year later, not in the report.
Answer as per the official UPSC answer key.
Which one of the following observations is *not* true about the Quit India Movement of 1942 ?
Answer (b) & explanation
It was led by Mahatma Gandhi is the observation 'not true' per UPSC's key (b). Gandhi gave the 'Do or Die' call at Gowalia Tank on 8 August 1942, but he and the whole Congress leadership were arrested the next morning (Operation Zero Hour). The movement then ran leaderless and spontaneous, so (c) is true. (a) is arguable: it began as a non-violent call, though it later saw sabotage and violence. (d) is true in UPSC's view: the organised labour class largely stayed away, partly because the Communists opposed it after the USSR joined the war.
Notice the leaders who stepped in: Aruna Asaf Ali hoisted the flag, Usha Mehta ran Congress Radio, and parallel governments rose in Ballia, Tamluk and Satara.
Answer as per the official UPSC answer key.
Read the passage
A country under foreign domination seeks escape from the present in dreams of a vanished age, and finds consolation in visions of past greatness. That is a foolish and dangerous pastime in which many of us indulge. An equally questionable practice for us in India is to imagine that we are still spiritually great though we have come down in the world in other respects. Spiritual or any other greatness cannot be founded on lack of freedom and opportunity, or on starvation and misery. Many western writers have encouraged that notion that Indians are other-worldly. I suppose the poor and unfortunate in every country become to some extent other-worldly, unless they become revolutionaries, for this world is evidently not meant for them. So also subject peoples.
As a man grows to maturity he is not entirely engrossed in, or satisfied with, the external objective world. He seeks also some inner meaning, some psychological and physical satisfactions. So also with peoples and civilizations as they mature and grow adult. Every civilization and every people exhibit these parallel streams of an external life and an internal life. Where they meet or keep close to each other, there is an equilibrium and stability. When they diverge conflict arises and the crises that torture the mind and spirit.
According to the passage, the torture of the mind and spirit is caused
Answer (c) & explanation
Lack of equilibrium between external and internal life is correct (c). Step 1: find the phrase. The passage says every people has 'parallel streams of an external life and an internal life'. Step 2: 'Where they meet or keep close to each other, there is an equilibrium and stability. When they diverge conflict arises and the crises that torture the mind and spirit.' So the cause is the loss of balance between the two lives: (c). Step 3: (a) and (b) mention foreign domination, which appears in the first paragraph, not as the cause of this torture. (d) is invented. So (a), (b) and (d) fail.
Tip: when a question quotes a phrase, find that exact phrase and read the sentence just before it. The cause is usually right there.
Answer as per the official UPSC answer key.
(Same information as the question above.)
How many females were not in favour of the proposal?
Answer (a) & explanation
430 is correct (a). Step 1: 'not in favour' here means those who voted against, as UPSC's key takes it. Step 2: females against = total against − males against = 1,226 − 796 = 430. Step 3: if you also added the 196 undecided females, you would get 626, which is not an option, confirming the intended reading. (b), (c) and (d) do not match. So (b), (c) and (d) fail.
Tip: when a phrase is ambiguous ('not in favour' could include undecided), check which reading gives an option. The options often tell you the intended meaning.
Answer as per the official UPSC answer key.
India is regarded as a country with “Demographic Dividend”. This is due to
Answer (b) & explanation
The answer is (b). A demographic dividend is the economic growth potential that arises when a large share of the population is of working age (15-64), with fewer dependants (children and elderly) to support. More workers, savings and investment can speed up growth, provided they are healthy, educated and employed. Option (a), a high under-15 population, means a high dependency burden. Option (c), many elderly, means an ageing society, like Japan. Option (d), a high total population, is not by itself a dividend.
Notice India's position: about two-thirds of Indians are of working age, and the median age is around 28-29. India's dividend window is expected to last until about the 2040s. To reap it, India needs skilling (Skill India, PMKVY), quality education, health and jobs; otherwise it becomes a 'demographic disaster'. India became the world's most populous country in 2023. Trap: working-age share, not total size, defines the dividend.
Answer as per the official UPSC answer key.
There is a concern over the increase in harmful algal blooms in the seawaters of India. What could be the causative factors for this phenomenon ?
- 1. Discharge of nutrients from the estuaries.
- 2. Run-off from the land during the monsoon.
- 3. Upwelling in the seas.
Select the correct answer from the codes given below :
Answer (d) & explanation
All three are correct (d). Harmful algal blooms grow when seawater gets extra nutrients, mainly nitrogen and phosphorus. Estuaries discharge sewage and fertiliser-laden river water into the sea (1). Monsoon run-off washes soil and fertilisers off the land (2). Upwelling brings cold, nutrient-rich deep water to the sunlit surface (3), as off the Kerala coast in the monsoon. So options (a), (b) and (c) leave out real causes.
Notice the wider idea: this process is eutrophication. Blooms such as Noctiluca in the Arabian Sea can create oxygen-poor dead zones and fish kills, and some algae release toxins. Warming seas make blooms more frequent. Trap: upwelling is natural, yet it is still a nutrient source.
Answer as per the official UPSC answer key.
In the context of Indian economy, consider the following statements :
- 1. The growth rate of GDP has steadily increased in the last five years.
- 2. The growth rate in per capita income has steadily increased in the last five years.
Which of the statements given above is/are correct ?
Answer (d) & explanation
Neither statement is correct (d). In the five years to 2010–11, India's GDP growth did not rise steadily: it was about 9.6% in 2006–07 and 9.3% in 2007–08, then fell to about 6.7% in 2008–09 after the global financial crisis, before recovering to around 8–9%. Per capita income growth followed the same ups and downs (2). So (a), (b) and (c) fail.
Notice the method: UPSC often uses 'steadily' to test whether you know a dip occurred. GDP data have since been revised to the 2011–12 base, and a new 2022–23 base series is being introduced. Per capita income growth is roughly GDP growth minus population growth. Trap: high average growth is not the same as steady increase.
Answer as per the official UPSC answer key.
Consider the following three statements:
- 1. Only students can participate in the race.
- 2. Some participants in the race are girls.
- 3. All girl participants in the race are invited for coaching.
Which one of the following conclusions can be drawn from the above statements?
Answer (c) & explanation
All participants are students is correct (c). Step 1: 'Only students can participate' means every participant is a student. That is option (c), drawn directly. Step 2: check (a). Only girl participants are invited for coaching; boys who participate may not be. So 'all participants are invited' goes too far. Step 3: check (b). Not every student takes part in the race, and only girl participants are invited, so 'all students are invited' is also wrong. So (a), (b) and (d) fail.
Tip: 'only A can do B' means 'everyone who does B is A'. Turn 'only' into 'all ... are' and the answer pops out.
Answer as per the official UPSC answer key.
If a bus travels 160 km in 4 hours and a train travels 320 km in 5 hours at uniform speeds, then what is the ratio of the distances travelled by them in one hour?
Answer (b) & explanation
5 : 8 is correct (b). Step 1: the bus covers 160 km in 4 hours, so in one hour it covers 160 ÷ 4 = 40 km. Step 2: the train covers 320 km in 5 hours, so in one hour it covers 320 ÷ 5 = 64 km. Step 3: the ratio is 40 : 64. Divide both by 8: 5 : 8. (a) reverses the order, a common trap. So (a), (c) and (d) fail.
Tip: always keep the ratio in the order the question asks (bus first, train second). Reversed answers are always among the options.
Answer as per the official UPSC answer key.
Directions: each item describes a situation and is followed by four possible responses. Indicate the response you find most appropriate. There is no penalty for wrong answers for these items. You have been asked to give an explanation for not attending an important official meeting. Your immediate boss who has not informed you about the meeting is now putting pressure on you not to place an allegation against him/her. You would
Answer (a) & explanation
UPSC's key lists two responses (a) and (b), and these items carried no negative marking. Step 1: the boss did not inform you, and now pressures you to hide this. Step 2: (a) sending a written reply that states the facts, and (b) explaining the situation to the top boss in person, both keep to the truth without making accusations beyond the facts. Step 3: (c) is wrong: admitting a fault that is not yours is dishonest. (d) is wrong: blaming the coordinator shifts responsibility unfairly.
Tip: for these interpersonal items, pick the response that is lawful, honest and keeps the public work going. Avoid options that give in to pressure, pass the buck or abandon duty.
Answer as per the official UPSC answer key.
With reference to India, consider the following Central Acts :
- 1. Import and Export (Control) Act, 1947
- 2. Mining and Mineral Development (Regulation) Act, 1957
- 3. Customs Act, 1962
- 4. Indian Forest Act, 1927
Which of the above Acts have relevance to/bearing on the biodiversity conservation in the country ?
Answer (c) & explanation
All four Acts are relevant (c). The Import and Export (Control) Act, 1947 (now replaced by the Foreign Trade Act, 1992) and the Customs Act, 1962 regulate the movement of wildlife, plants and biological material across borders, helping enforce CITES and stop smuggling (1, 3). The Mines and Minerals (Development and Regulation) Act, 1957 governs mining, which affects forests and habitats and requires environmental clearances (2). The Indian Forest Act, 1927 protects forests through reserved and protected forests (4). So options (a), (b) and (d) fail.
Notice the core law: the Biological Diversity Act, 2002, amended in 2023, set up the National Biodiversity Authority (Chennai), State Biodiversity Boards and local Biodiversity Management Committees. Other key laws are the Wildlife (Protection) Act, 1972 (amended 2022) and the Forest (Conservation) Act, 1980, renamed Van (Sanrakshan Evam Samvardhan) Adhiniyam in 2023. Trap: trade laws also protect biodiversity.
Answer as per the official UPSC answer key.