UPSC Prelims PYQs with explanations
Real questions from official papers, mapped to syllabus topics. Attempt each one; the answer and the reason appear instantly.
Which one of the following best defines the term 'State'?
Answer (a) & explanation
Option (a) best defines the State (a). Political science names four elements of a State: population, territory, government and sovereignty. Option (a) has all four: a community of persons (population), a definite territory, independence from external control (sovereignty) and an organised government. Option (b) leaves out sovereignty and adds aims such as protecting natural rights. Option (c) describes a nation or community with shared culture, and also misses sovereignty. Option (d) adds features, such as an independent judiciary, that a State need not have.
Notice the difference between State and nation: a nation is a people with a shared identity; a State is a political body. Under Article 12, "State" in India also covers bodies like Parliament and local authorities.
(b) is long and sounds complete, but it never mentions independence from outside control.
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Answer as per the official UPSC answer key.
Read the passage
A social and physical environment riddled with poverty, inequities, unhygienic and insanitary conditions generates the risk of infectious diseases. Hygiene has different levels : personal, domestic and community hygiene. There is no doubt that personal cleanliness brings down the rate of infectious diseases. But the entry of the market into this domain has created a false sense of security that gets conditioned and reinforced by the onslaught of advertisements. Experience in Western Europe shows that along with personal hygiene, general improvements in environmental conditions and components like clean water, sanitation and food security have brought down infant/child death/infection rates considerably. The obsession with hand hygiene also brings in the persisting influence of the market on personal health, overriding or marginalising the negative impact on ecology and the emergence of resistant germs.
On the basis of the passage given above, the following assumptions have been made :
- 1. People who are obsessed with personal hygiene tend to ignore the community hygiene.
- 2. Emergence of multi-drug resistant germs can be prevented by personal cleanliness.
- 3. Entry of the market in the domain of hygiene increases the risk of infectious diseases.
- 4. Scientific and micro-level interventions are not sufficient to bring down the burden of infectious diseases.
- 5. It is community hygiene implemented through public health measures that is really effective in the battle against infectious diseases.
Which of the above assumptions are valid ?
Answer (c) & explanation
Assumptions 4 and 5 are valid (c). Step 1: the passage says Western Europe cut infections through clean water, sanitation, food security and hygiene for all. So small-scale, personal steps are not enough (4), and community hygiene through public health works (5). Step 2: assumption 3 says the market raises the risk. The passage says the market creates a false sense of security, not higher risk. Step 3: assumption 2 says personal cleanliness can prevent drug-resistant germs; not supported. Assumption 1 is also not stated. So options (a), (b) and (d) fail.
Tip: "false sense of security" is not the same as "increased risk". Check the exact claim, not just the topic.
Answer as per the official UPSC answer key.
Half of the villagers of a certain village have their own houses. One-fifth of the villagers cultivate paddy. One-third of the villagers are literate. Four-fifth of the villagers are under 25 years of age. Which one of the following statements is certainly correct ?
Answer (b) & explanation
The statement certainly correct is that some villagers under 25 are literate (b). Step 1: four-fifths are under 25 and one-third are literate. Add them: 4/5 + 1/3 = 17/15, which is more than the whole village. Step 2: two groups that together exceed the total must overlap. So some literate villagers must be under 25. That is (b). Step 3: options (a), (c) and (d) link houses, paddy and age in exact ways. The data give no such link, so none is certain.
Tip: if two fractions of the same group add up to more than 1, the groups must share members. The overlap is at least the excess (here 2/15).
Answer as per the official UPSC answer key.
If the price of an article is decreased by 20% and then the new price is increased by 25%, then what is the net change in the price ?
Answer (a) & explanation
There is no net change, 0% (a). Step 1: a 20% cut means multiplying by 0.8. Step 2: a 25% rise on the new price means multiplying by 1.25. Step 3: 0.8 × 1.25 = 1. So the final price equals the starting price. Options (b) and (c) wrongly add or subtract the percentages (25 − 20 = 5). Option (d) is wrong because the multipliers settle it without knowing the price.
Tip: for successive percentage changes, multiply the factors. A shortcut is a + b + ab/100: −20 + 25 − 500/100 = 0.
don't just add –20 and +25. The 25% is taken on the reduced price.
Answer as per the official UPSC answer key.
Which of the following have species that can establish symbiotic relationship with other organisms?
- 1. Cnidarians
- 2. Fungi
- 3. Protozoa
Select the correct answer using the code given below.
Answer (d) & explanation
All three groups have symbiotic species (d). Symbiosis is a close, long-term relationship between two different species. Item 1 is right: corals, which are cnidarians, host algae called zooxanthellae that give them food and colour; losing them causes coral bleaching. Item 2 is right: fungi form mycorrhizae with plant roots, helping them absorb water and phosphorus, and they team up with algae as lichens. Item 3 is right: protozoa in a termite's gut digest the cellulose in the wood it eats.
Notice the types of symbiosis: mutualism (both gain), commensalism (one gains, the other is unaffected) and parasitism (one gains at the other's cost). Rhizobium bacteria in legume roots are another mutualism.
Answer as per the official UPSC answer key.
The black cotton soil of India has been formed due to the weathering of
Answer (b) & explanation
Black cotton soil formed from fissure volcanic rock (b). Black (regur) soil formed from the weathering of basalt lava that poured out through long fissures about 66 million years ago to build the Deccan Traps. It is rich in iron, lime, magnesium and potash, but poor in nitrogen and phosphorus. It holds moisture well, swells when wet and cracks when dry, so it ploughs itself. It suits cotton, hence its name. Brown forest soil (a), granite and schist (c), and shale and limestone (d) give rise to other soils.
Notice that black soil covers much of Maharashtra, western Madhya Pradesh and Gujarat. Red soil forms from granite and gneiss, and laterite from heavy leaching.
Answer as per the official UPSC answer key.
Consider the following statements in respect of the 32nd Summer Olympics :
- 1. The official motto for this Olympics is ‘A New World’.
- 2. Sport Climbing, Surfing, Skateboarding, Karate and Baseball are included in this Olympics.
Which of the above statements is/are correct?
Answer (b) & explanation
Only statement 2 is correct (b). Statement 1 is wrong: the Tokyo 2020 Games, the 32nd Summer Olympics, held in 2021 because of COVID, had the motto "United by Emotion", not "A New World". The IOC also added "Together" to the Olympic motto, making it "Faster, Higher, Stronger – Together". Statement 2 is right: Tokyo added sport climbing, surfing, skateboarding and karate, and brought back baseball/softball.
Notice India's best Olympics till then: seven medals at Tokyo, including Neeraj Chopra's gold in javelin, India's first in athletics. At Paris 2024, India won six medals, and breaking made its debut. The 2028 Games are in Los Angeles.
Answer as per the official UPSC answer key.
Seven books P, Q, R, S, T, U and V are placed side by side. R, Q and T have blue covers and other books have red covers. Only S and U are new books and the rest are old. P, R and S are law reports; the rest are Gazetteers. Books of old Gazetteers with blue covers are
Answer (c) & explanation
The old Gazetteers with blue covers are Q and T (c). Step 1: list each group. Gazetteers: all except the law reports P, R and S, so Q, T, U, V. Step 2: old books: all except the new ones S and U, so P, Q, R, T, V. Blue covers: Q, R, T. Step 3: books in all three groups: Q and T. Option (a) includes R, a law report. Options (b) and (d) include U, a new book.
Tip: in grouping puzzles, write each list and find the common members. Using "all except" lists helps avoid errors when a group is described by what it is not.
Answer as per the official UPSC answer key.
At which one of the following times, do the hour hand and the minute hand of the clock make an angle of 180° with each other ?
Answer (d) & explanation
The hands are opposite between 7:05 and 7:10 (d). Step 1: the angle between the hands is |30H − 5.5M|, where H is the hour and M the minutes. At 7:00 it is 30 × 7 = 210°, so (a) fails. Step 2: as minutes pass, the minute hand closes the gap at 5.5° per minute. We need 210 − 5.5M = 180, so M = 30 ÷ 5.5 ≈ 5.45 minutes. Step 3: so the hands are 180° apart at about 7:05:27. That is just after 7:05, so (b) and (c) fail.
Tip: the minute hand gains 5.5° per minute on the hour hand. This one fact solves most clock-angle questions.
at 7:00 the angle is 210°, not 180°. The minute hand has to catch up 30°.
Answer as per the official UPSC answer key.
Which one of the following effects of creation of black money in India has been the main cause of worry to the Government of India?
Answer (d) & explanation
The main worry is loss of tax revenue (d). Black money is income hidden from the tax authorities, whether earned legally or illegally. All four options describe real effects, but the government's main concern is the loss of revenue from tax evasion, which shrinks its ability to spend on health, education and infrastructure, and forces honest taxpayers to carry more of the load. Options (a) and (b) describe where black money is parked, such as real estate, gold and jewellery. Option (c) describes its political misuse.
Notice the White Paper on Black Money (2012), the Black Money (Undisclosed Foreign Income and Assets) Act, 2015, and demonetisation of ₹500 and ₹1,000 notes in November 2016.
Answer as per the official UPSC answer key.
With reference to the history of ancient India, Bhavabhuti, Hastimalla and Kshemeshvara were famous
Answer (b) & explanation
All three were playwrights (b). They wrote Sanskrit plays. Bhavabhuti (8th century, court of Yashovarman of Kanauj) wrote Uttararamacharita, Mahaviracharita and Malatimadhava, and is often ranked next to Kalidasa. Hastimalla was a Jain dramatist of the Karnataka region, around the 13th century, who wrote plays on Jain and epic themes. Kshemishvara of Kanauj wrote Chandakaushika (10th century) on King Harishchandra. Option (a) is a trap: Hastimalla was a Jain, but not a monk. They were not architects (c) or chiefly philosophers (d).
Notice other Sanskrit dramatists: Bhasa, Shudraka (Mrichchhakatika), Vishakhadatta (Mudrarakshasa) and Harsha himself (Ratnavali, Nagananda, Priyadarshika).
Hastimalla was a Jain, but he is remembered as a playwright, not a monk.
Answer as per the official UPSC answer key.
‘Triclosan’, considered harmful when exposed to high levels for a long time, is most likely present in which of the following?
Answer (d) & explanation
Triclosan is most likely in toiletries (d). Triclosan is an antibacterial and antifungal agent added to soaps, toothpastes, deodorants, hand washes and some cosmetics. Long exposure at high levels is linked to hormone disruption, especially of thyroid hormones, and to germs becoming resistant to antibiotics. It also builds up in rivers and harms aquatic life. It is not used in food preservatives (a), fruit-ripening agents (b) such as calcium carbide or ethylene, or in reused plastic containers (c).
Notice that the US FDA banned triclosan in consumer antiseptic hand washes in 2016. Notice related concerns: antimicrobial resistance (AMR), which India tackles under its National Action Plan on AMR.
Answer as per the official UPSC answer key.
Read the passage
Researchers were able to use stem cells to gauge the neurotoxic effects of the environmental pollutant Bisphenol A (BPA). They used a combination of biochemical and cell-based assays to examine the gene expression profile during the differentiation of mouse embryonic stem cells upon treatment with BPA, a compound known to cause heart diseases, diabetes, and developmental abnormalities in humans. They were able to detect and measure BPA toxicity towards the proper specification of primary germ layers, such as endoderm and ectoderm, and the establishment of neural progenitor cells.
On the basis of the passage given above, the following assumptions have been made :
- 1. BPA may alter embryonic development in vivo.
- 2. Biochemical and cell-based assays are useful in finding out treatments for pollution-induced diseases.
- 3. Embryonic stem cells could serve as a model to evaluate the physiological effects of environmental pollutants.
Which of the above assumptions are valid ?
Answer (c) & explanation
Assumptions 1 and 3 are valid (c). Step 1: the passage says BPA (a chemical in some plastics) harmed the formation of germ layers in stem cells. Germ layers are the first steps of an embryo's growth. So BPA may alter embryo development in the body (1). Step 2: the study used embryonic stem cells as a test model. So they can serve as a model to study pollutants (3). Step 3: assumption 2 says the assays help find treatments. But the assays measured toxicity; treatments are not discussed. So options (a), (b) and (d) fail.
Tip: "in vivo" means in a living body; "in vitro" means in a lab dish. Separate what a study measured from what it might later lead to.
Answer as per the official UPSC answer key.
Consider all 3-digit numbers (without repetition of digits) obtained using three non-zero digits which are multiples of 3. Let S be their sum. Which of the following is/are correct ?
- 1. S is always divisible by 74.
- 2. S is always divisible by 9.
Select the correct answer using the code given below :
Answer (c) & explanation
Both statements are correct (c). Step 1: the non-zero digits that are multiples of 3 are 3, 6 and 9. Without repeating digits, they make 3 × 2 × 1 = 6 numbers. Step 2: each digit appears in each place (hundreds, tens, units) twice. So S = 2 × (3 + 6 + 9) × 111 = 36 × 111 = 3996. Step 3: 3996 = 74 × 54, so it is divisible by 74 (statement 1). Its digits add up to 27, so it is divisible by 9 (statement 2). So options (a), (b) and (d) fail.
Tip: for the sum of all numbers made from given digits, use (number of times each digit sits in a place) × (sum of digits) × 111.
Answer as per the official UPSC answer key.
A cubical vessel of side 1 m is filled completely with water. How many millilitres of water is contained in it (neglect thickness of the vessel) ?
Answer (d) & explanation
The vessel holds 10,00,000 ml (d). Step 1: the vessel is a cube of side 1 m, so its volume is 1 m³. Step 2: 1 m³ = 1000 litres. Step 3: 1 litre = 1000 ml. So 1000 × 1000 = 10,00,000 ml (one million). Option (a), 1000, is the number of litres, not millilitres. Options (b) and (c) drop zeroes.
Tip: remember 1 m³ = 1000 litres and 1 cm³ = 1 ml. So 1 m³ = 100 × 100 × 100 cm³ = 10,00,000 ml.
1000 is the answer in litres. The question asks for millilitres.
Answer as per the official UPSC answer key.
In the nature, which of the following is/are most likely to be found surviving on a surface without soil?
- 1. Fern
- 2. Lichen
- 3. Moss
- 4. Mushroom
Select the correct answer using the code given below.
Answer (c) & explanation
Lichens and mosses survive on surfaces without soil (c). Lichens, a partnership of a fungus and an alga or cyanobacterium, and mosses are the pioneer species on bare rock. They cling to the surface, release acids that slowly break it down, and trap dust and dead matter, which starts soil formation. This begins primary succession. Item 1 is wrong: ferns have roots that need some soil. Item 4 is wrong: mushrooms are fungi that need dead organic matter to feed on.
Notice that lichens are indicators of clean air: they disappear where sulphur dioxide pollution is high. The final stable community in succession is the climax community, such as a forest.
Answer as per the official UPSC answer key.
With reference to India, Didwana, Kuchaman, Sargol and Khatu are the names of
Answer (d) & explanation
They are saline lakes (d). Didwana, Kuchaman, Sargol and Khatu are saline lakes in the Thar region of Rajasthan, along with the larger Sambhar, India's biggest inland salt lake. These lakes fill in the monsoon and dry out in summer, leaving salt that is harvested as common salt. They are not glaciers (a), which are in the Himalaya; not mangrove areas (b), which are on the coasts; and, apart from Sambhar, not Ramsar sites (c).
Notice that Sambhar is a Ramsar site (1990), known for flamingos and a mass bird death from avian botulism in 2019. Rajasthan's inland drainage includes the Luni, which ends in the Rann of Kachchh.
Answer as per the official UPSC answer key.
With reference to Indian judiciary, consider the following statements :
- 1. Any retired judge of the Supreme Court of India can be called back to sit and act as a Supreme Court judge by the Chief Justice of India with prior permission of the President of India.
- 2. A High Court in India has the power to review its own judgement as the Supreme Court does.
Which of the statements given above is/are correct?
Answer (a) & explanation
Only statement 1 is correct (a). Statement 1 is right: Article 128 lets the Chief Justice of India, with the President's previous consent, request a retired Supreme Court judge to sit and act as a judge again. Statement 2 turns on the words "as the Supreme Court does". Article 137 gives the Supreme Court an express power to review its own judgments. The Constitution has no matching article for High Courts, which draw review power from the Code of Civil Procedure and their status as courts of record. So UPSC treated statement 2 as wrong.
Notice the matching rule for High Courts: Article 224A lets a Chief Justice ask a retired High Court judge to sit again. The Supreme Court revived this to clear pending cases in 2021.
read statement 2 as a question about the text of the Constitution. Article 137 has no High Court twin.
Answer as per the official UPSC answer key.
A Statement followed by Conclusion-I and Conclusion-II is given below. You have to take the Statement to be true even if it seems to be at variance from the commonly known facts. Read all Conclusions and then decide which of the given Conclusion(s) logically follows/follow from the Statement, disregarding the commonly known facts.
Statement : Some cats are almirahs. Some almirahs are chairs. All chairs are tables.
Conclusion-I : Certainly some almirahs are tables.
Conclusion-II : Some cats may not be chairs.
Which one of the following is correct ?
Answer (c) & explanation
Both conclusions follow (c). Step 1: some almirahs are chairs, and all chairs are tables. So those almirahs are also tables. Conclusion I, "certainly some almirahs are tables", is true. Step 2: nothing links cats to chairs directly. So it is possible that some cats are not chairs. Conclusion II uses "may not", which only claims a possibility. Step 3: so both follow. Options (a), (b) and (d) fail.
Tip: "may" or "may not" conclusions follow whenever the case is possible and not ruled out. "Certainly" conclusions need a firm chain, like "some A are B, all B are C".
a 'may' conclusion follows whenever the statements leave that case open.
Answer as per the official UPSC answer key.
Consider two Statements and a Question :
Statement-1 : The last day of the month is a Wednesday.
Statement-2 : The third Saturday of the month was the seventeenth day.
Question : What day is the fourteenth of the given month ?
Which one of the following is correct in respect of the Statements and the Question ?
Answer (b) & explanation
Statement-2 alone is sufficient (b). Step 1: Statement-2 says the third Saturday was the 17th. The 14th is 3 days earlier. Three days before Saturday is Wednesday. So Statement-2 alone answers it. Step 2: Statement-1 says the last day is a Wednesday. But we do not know whether the month has 28, 29, 30 or 31 days. So the 14th could fall on different days. Step 3: so (a) fails, and since Statement-2 works alone, (c) and (d) fail too.
Tip: a fixed date with a known weekday is the best anchor. A clue about "the last day" fails when the month's length is unknown.
Answer as per the official UPSC answer key.