UPSC Prelims PYQs with explanations
Real questions from official papers, mapped to syllabus topics. Attempt each one; the answer and the reason appear instantly.
Consider the following pairs :
| Country | Important reason for being in the news recently
| 1. Chad | Setting up of permanent military base by China
| 2. Guinea | Suspension of Constitution and Government by military
| 3. Lebanon | Severe and prolonged economic depression
| 4. Tunisia | Suspension of Parliament by President
How many pairs given above are correctly matched ?
Answer (c) & explanation
Three pairs are correctly matched (c). Pair 2 is right: Guinea's army ousted President Condé in September 2021 and suspended the constitution. Pair 3 is right: the World Bank called Lebanon's economic collapse, from 2019, one of the worst anywhere since the mid-19th century. Pair 4 is right: Tunisia's President Kais Saied suspended parliament in July 2021. Pair 1 is wrong: Chad was in the news for President Idriss Déby's death in 2021 and military rule; China has no base there. China's only acknowledged overseas military base is in Djibouti, opened in 2017.
Notice the wave of coups in Africa's Sahel and west: Mali, Burkina Faso, Guinea and Niger, many turning away from France and towards Russia.
Answer as per the official UPSC answer key.
X and Y run a 3 km race along a circular course of length 300 m. Their speeds are in the ratio 3 : 2. If they start together in the same direction, how many times would the first one pass the other (the start-off is not counted as passing)?
Answer (b) & explanation
X passes Y 3 times (b). Step 1: the race is 3 km = 3000 m on a 300 m track. So X runs 10 rounds. Step 2: the speeds are 3 : 2, so in the same time Y runs 2/3 × 10 = 6⅔ rounds. Step 3: X gains 10 − 6⅔ = 3⅓ rounds over Y. Each full round gained is one pass. So X passes Y 3 times. Options (a), (c) and (d) miscount; the extra ⅓ round is not a full pass.
Tip: on a circular track, the number of passes = the number of full laps the faster runner gains. The start is not counted.
Answer as per the official UPSC answer key.
A person X wants to distribute some pens among six children A, B, C, D, E and F. Suppose A gets twice the number of pens received by B, three times that of C, four times that of D, five times that of E and six times that of F. What is the minimum number of pens X should buy so that the number of pens each one gets is an even number?
Answer (c) & explanation
The minimum is 294 pens (c). Step 1: A gets 2, 3, 4, 5 and 6 times the others. So A must be divisible by all of them: a multiple of 60. Step 2: every share must also be even. With A = 60, B = 30, C = 20, D = 15 (odd). So A must be a multiple of 120. Step 3: with A = 120: B = 60, C = 40, D = 30, E = 24, F = 20. Total = 120 + 60 + 40 + 30 + 24 + 20 = 294. Option (a), 147, is the total for A = 60, which gives odd shares.
Tip: after finding the LCM, check the extra condition (even shares). Doubling the base often fixes it.
147 (with A = 60) is the answer if you ignore "even". Then D gets 15.
Answer as per the official UPSC answer key.
What is the number of numbers of the form 0.XY, where X and Y are distinct non-zero digits?
Answer (a) & explanation
There are 72 such numbers (a). Step 1: X can be any non-zero digit: 9 choices (1 to 9). Step 2: Y must be non-zero and different from X: 8 choices. Step 3: 9 × 8 = 72. Option (b), 81, allows X and Y to be the same. Options (c) and (d) include zero, which the question rules out. Note that X and Y are only the two decimal places, so 0.XY always has exactly two digits after the point.
Tip: "distinct" removes one choice for the second place. "Non-zero" removes 0 from both places.
Answer as per the official UPSC answer key.
With reference to “Software as a Service (SaaS)”, consider the following statements :
- 1. SaaS buyers can customise the user interface and can change data fields.
- 2. SaaS users can access their data through their mobile devices.
- 3. Outlook, Hotmail and Yahoo! Mail are forms of SaaS.
Which of the statements given above are correct ?
Answer (d) & explanation
All three statements are correct (d). In Software as a Service, the provider hosts the software in the cloud, and users reach it through a browser or app. Statement 1 is right: buyers can usually configure the user interface and change data fields to suit their needs. Statement 2 is right: users can reach their data from any device, including mobiles, over the internet. Statement 3 is right: webmail services such as Outlook, Hotmail and Yahoo! Mail are everyday examples of SaaS.
Notice the three cloud layers: SaaS (ready software, such as Gmail), PaaS (Platform as a Service, a platform for developers) and IaaS (Infrastructure as a Service, raw servers and storage). India's government cloud initiative is MeghRaj.
Answer as per the official UPSC answer key.
Consider the following :
- 1. Asian Infrastructure Investment Bank
- 2. Missile Technology Control Regime
- 3. Shanghai Cooperation Organisation
India is a member of which of the above ?
Answer (d) & explanation
India is a member of all three (d). Item 1 is right: India is a founding member of the Asian Infrastructure Investment Bank, which began work in 2016 in Beijing, and is its second-largest shareholder after China, as well as its largest borrower. Item 2 is right: India joined the Missile Technology Control Regime in June 2016, which helps it buy and sell missile technology. Item 3 is right: India became a full member of the Shanghai Cooperation Organisation in 2017, along with Pakistan. So options (a), (b) and (c) all leave something out.
Notice India's place in the export control clubs: it is in the MTCR, the Wassenaar Arrangement (2017) and the Australia Group (2018), but its bid for the Nuclear Suppliers Group stays blocked by China.
AIIB is led by China, so many assume India stayed out. India is in fact its largest borrower.
UPSC repeats traps like this year after year. The PYQ Book gathers every trap in one place, so you see them coming. Try the free sample
Answer as per the official UPSC answer key.
Consider the following statements :
DNA Barcoding can be a tool to:
- 1. assess the age of a plant or animal.
- 2. distinguish among species that look alike.
- 3. identify undesirable animal or plant materials in processed foods.
Which of the statements given above is/are correct ?
Answer (d) & explanation
Statements 2 and 3 are correct (d). DNA barcoding reads a short, standard stretch of a gene that differs between species, much like a barcode at a shop. In animals this is usually the COI gene of mitochondria. Statement 2 is right: it can tell apart look-alike species, such as cryptic insects or fish fillets. Statement 3 is right: it can find hidden or undesirable plant or animal material in processed foods, such as pork in a "beef" product, or adulteration in herbal medicines. Statement 1 is wrong: the barcode tells you which species something is, not its age.
Notice its use in wildlife crime: barcoding helps identify seized animal parts, such as pangolin scales, and protects food safety and trade.
Answer as per the official UPSC answer key.
On one side of a 1·01 km long road, 101 plants are planted at equal distance from each other. What is the total distance between 5 consecutive plants?
Answer (b) & explanation
The distance is 40.4 m (b). Step 1: 101 plants in a line leave 100 gaps between them. The road is 1.01 km = 1010 m. Step 2: so each gap = 1010 ÷ 100 = 10.1 m. Step 3: 5 plants in a row have 4 gaps between them. 4 × 10.1 = 40.4 m. Option (d), 50.5 m, counts 5 gaps. Options (a) and (c) use 10 m per gap.
Tip: n posts in a line have n − 1 gaps. This "fence-post" rule is a common UPSC trap.
5 plants have 4 gaps, not 5.
Answer as per the official UPSC answer key.
What is the remainder when 91 × 92 × 93 × 94 × 95 × 96 × 97 × 98 × 99 is divided by 1261?
Answer (d) & explanation
The remainder is 0 (d). Step 1: break the divisor into factors: 1261 = 13 × 97. Step 2: look for these factors in the product. 91 = 7 × 13, so 13 is there. 97 itself is one of the numbers. Step 3: so the product is divisible by 13 × 97 = 1261, and the remainder is 0. Options (a), (b) and (c) assume some remainder is left.
Tip: when dividing a long product, first factorise the divisor. If all its factors appear in the product, the remainder is zero.
Answer as per the official UPSC answer key.
With reference to the Indian economy, consider the following statements :
- 1. A share of the household financial savings goes towards government borrowings.
- 2. Dated securities issued at market-related rates in auctions form a large component of internal debt.
Which of the above statements is/are correct ?
Answer (c) & explanation
Both statements are correct (c). Statement 1 is right: household savings kept in banks, insurance, provident funds and small savings schemes are partly lent to the government, because these institutions buy G-Secs, and small savings funds go into the National Small Savings Fund. Statement 2 is right: dated securities, long-term bonds sold through RBI auctions at market rates, are the largest part of the Centre's internal debt, far ahead of Treasury Bills and other items.
Notice the difference: internal debt is owed within India; external debt is owed abroad. India's public debt is mostly internal and in rupees, which lowers risk. The RBI manages government borrowing as its debt manager.
Answer as per the official UPSC answer key.
In the context of WHO Air Quality Guidelines, consider the following statements :
- 1. The 24-hour mean of PM2·5 should not exceed 15 µg/m3 and annual mean of PM2·5 should not exceed 5 µg/m3.
- 2. In a year, the highest levels of ozone pollution occur during the periods of inclement weather.
- 3. PM10 can penetrate the lung barrier and enter the bloodstream.
- 4. Excessive ozone in the air can trigger asthma.
Which of the statements given above are correct ?
Answer (b) & explanation
Statements 1 and 4 are correct (b). Statement 1 is right: the 2021 WHO Air Quality Guidelines set PM2.5 at 15 µg/m³ for the 24-hour mean and 5 µg/m³ for the annual mean. Statement 2 is wrong: ground-level ozone forms when sunlight acts on pollutants, so it peaks in hot, sunny weather, not in bad weather. Statement 3 is wrong: PM2.5, not PM10, is fine enough to pass the lung barrier into the bloodstream. Statement 4 is right: excess ozone irritates airways and can trigger asthma.
Notice that India's National Ambient Air Quality Standards (2009) are much looser: PM2.5 at 60 (24-hour) and 40 (annual). The National Clean Air Programme (2019) targets cuts in 131 cities.
PM10 reaches the lungs, but the bloodstream needs the finer PM2.5.
Answer as per the official UPSC answer key.
Which one of the following statements best describes the ‘Polar Code’ ?
Answer (a) & explanation
The Polar Code is a safety code for ships in polar waters (a). The International Code for Ships Operating in Polar Waters, adopted by the International Maritime Organization (IMO), came into force in 2017. It is binding through the SOLAS (safety) and MARPOL (pollution) conventions, and sets rules on ice-class ship design, crew training, equipment and strict limits on discharges in Arctic and Antarctic waters. Option (b) is wrong: Arctic boundaries are settled under UNCLOS and bilateral deals. Option (c) is wrong: research in Antarctica falls under the Antarctic Treaty (1959). Option (d) is wrong: the Arctic Council has no trade or security pact.
Notice why it matters now: melting ice is opening the Northern Sea Route, so traffic and the risk of spills are rising.
Answer as per the official UPSC answer key.
An Identity Card has the number ABCDEFG, not necessarily in that order, where each letter represents a distinct digit (1, 2, 4, 5, 7, 8, 9 only). The number is divisible by 9. After deleting the first digit from the right, the resulting number is divisible by 6. After deleting two digits from the right of original number, the resulting number is divisible by 5. After deleting three digits from the right of original number, the resulting number is divisible by 4. After deleting four digits from the right of original number, the resulting number is divisible by 3. After deleting five digits from the right of original number, the resulting number is divisible by 2. Which of the following is a possible value for the sum of the middle three digits of the number?
Answer (a) & explanation
1. Work from the left. The first 2 digits are divisible by 2, so the 2nd digit is even. The first 5 are divisible by 5, so the 5th digit is 5.
2. The first 4 digits must be divisible by 4 and the first 3 by 3. The first 6 must be divisible by 6, so the 6th digit is even. The digit sum 36 makes the whole number divisible by 9 automatically. Only two numbers pass every test: 7412589 and 1472589.
3. The middle three digits (3rd, 4th, 5th) add up to 1 + 2 + 5 = 8 in 7412589. (In the other number they give 14, which is not an option.)
"the first digit from the right" is the units digit. Read the deletions from the right carefully.
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Answer as per the official UPSC answer key.
Consider the Question and two Statements given below in respect of three cities P, Q and R in a State :
Question : How far is city P from city Q?
Statement-1 : City Q is 18 km from city R.
Statement-2 : City P is 43 km from city R.
Which one of the following is correct in respect of the Question and the Statements?
Answer (d) & explanation
Even both statements are not enough (d). Step 1: together we know Q is 18 km from R and P is 43 km from R. Step 2: we are not told the directions. If P and Q are on the same side of R, PQ could be 43 − 18 = 25 km. On opposite sides in a line, PQ could be 43 + 18 = 61 km. In other directions, anything in between. Step 3: so PQ cannot be fixed. Options (a), (b) and (c) fail.
Tip: two distances from a common point fix only a range for the third distance (between their difference and their sum).
Answer as per the official UPSC answer key.
There are two containers X and Y. X contains 100 ml of milk and Y contains 100 ml of water. 20 ml of milk from X is transferred to Y. After mixing well, 20 ml of the mixture in Y is transferred back to X. If m denotes the proportion of milk in X and n denotes the proportion of water in Y, then which one of the following is correct?
Answer (a) & explanation
m equals n (a). Step 1: both containers end with 100 ml. Whatever water ends up in X must equal the milk left in Y, because they swapped places. Step 2: check: Y has 100 ml water + 20 ml milk. 20 ml of this mix holds 16⅔ ml water and 3⅓ ml milk. Step 3: X now has 80 + 3⅓ = 83⅓ ml milk, and Y keeps 100 − 16⅔ = 83⅓ ml water. So m = n. Options (b), (c) and (d) fail.
Tip: in back-and-forth mixing with equal final volumes, the amount of each "foreign" liquid is always equal. No calculation is needed.
Answer as per the official UPSC answer key.
Which one of the following lakes of West Africa has become dry and turned into a desert ?
Answer (b) & explanation
Lake Faguibine has dried into desert (b). Lake Faguibine, near Timbuktu in Mali, was once one of West Africa's largest lakes, fed by the floodwaters of the Niger river. Droughts from the 1970s and weaker Niger floods have turned it into a dry, sandy basin. UNEP has used it as an example of climate-driven desertification. Lake Victoria (a) is in East Africa and is the continent's largest lake. Lake Oguta (c) in Nigeria still holds water. Lake Volta (d) in Ghana is one of the world's largest man-made reservoirs.
Notice Lake Chad, which has also shrunk by about 90% since the 1960s. The Great Green Wall initiative tries to halt the spread of the Sahara across the Sahel.
Answer as per the official UPSC answer key.
With reference to Indian history, consider the following pairs :
| Historical person | Known as
| 1. Aryadeva | Jaina scholar
| 2. Dignaga | Buddhist scholar
| 3. Nathamuni | Vaishnava scholar
How many pairs given above are correctly matched ?
Answer (c) & explanation
Two pairs are correct (c). Pair 1 is wrong: Aryadeva was a pupil of Nagarjuna and a leading Madhyamaka Buddhist philosopher, author of the Chatuhshataka, not a Jaina scholar. Pair 2 is right: Dignaga (5th–6th century) is called the founder of Buddhist logic, and his work shaped Dharmakirti after him. Pair 3 is right: Nathamuni (10th century) collected the Alvar hymns into the Nalayira Divya Prabandham and is counted the first Sri Vaishnava acharya, a line later led by Yamunacharya and Ramanuja.
Notice the pattern: UPSC keeps asking about thinkers of Buddhism (Nagarjuna, Asanga, Vasubandhu, Dignaga) and the Bhakti acharyas (Nathamuni, Ramanuja, Madhva). Group them by school, and such pair questions become easy marks.
Answer as per the official UPSC answer key.
Consider the following pairs :
| Region often mentioned in the news | Country
| 1. Anatolia | Turkey
| 2. Amhara | Ethiopia
| 3. Cabo Delgado | Spain
| 4. Catalonia | Italy
How many pairs given above are correctly matched?
Answer (b) & explanation
Two pairs are correctly matched (b). Pair 1 is right: Anatolia, or Asia Minor, is the large Asian part of Turkey. Pair 2 is right: Amhara is a region of Ethiopia that was drawn into the Tigray war (2020–22) and later saw its own fighting. Pair 3 is wrong: Cabo Delgado is a province of Mozambique, rich in natural gas and hit by an Islamist insurgency since 2017. Pair 4 is wrong: Catalonia, capital Barcelona, is in Spain, not Italy; its independence vote of 2017 caused a crisis.
Notice the method: such pairs test news geography. Place each region on a map with its country and the reason it was in the news, and you can answer even when the wording changes.
Answer as per the official UPSC answer key.
If the order of the letters in the English alphabet is reversed and each letter represents the letter whose position it occupies, then which one of the following represents 'LUCKNOW'?
Answer (d) & explanation
LUCKNOW becomes OFXPMLD (d). Step 1: in the reversed alphabet, A ↔ Z, B ↔ Y, and so on. A letter at place n becomes the letter at place 27 − n. Step 2: L (12) → O (15); U (21) → F (6); C (3) → X (24); K (11) → P (16). Step 3: N (14) → M (13); O (15) → L (12); W (23) → D (4). So the code is OFXPMLD. Option (c) ends in E and options (a), (b) start O-G; each has one wrong letter.
Tip: remember pairs that add to 27 (like EJOTY at 5, 10, 15, 20, 25). Check only the letters where options differ.
Answer as per the official UPSC answer key.
Six persons A, B, C, D, E and F are sitting equidistant from each other around a circular table (facing the centre of the table).
Consider the Question and two Statements given below :
Question : Who is sitting on the immediate left of A?
Statement-1 : B is sitting opposite to C and D is sitting opposite to E.
Statement-2 : F is sitting on the immediate left of B.
Which one of the following is correct in respect of the Question and the Statements?
Answer (d) & explanation
Even both statements are not enough (d). Step 1: Statement-1 says B faces C and D faces E. With six seats, A must face F. Step 2: Statement-2 says F is on B's immediate left. This fixes B and F side by side, and C ends up on A's right. Step 3: A's immediate left is then a seat held by D or E, and D and E can swap. So it cannot be fixed. Options (a), (b) and (c) fail.
Tip: in circular seating, check if any two people can swap without breaking a rule. If yes, the answer is not fixed.
Answer as per the official UPSC answer key.