CSAT (Paper II): previous-year questions
1280 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 400 of them came in the last five papers.
How often UPSC asks this
Questions per year, counted from the official papers.
Subtopics
Arrangements, ranking, ordering and puzzles
142 questions
Clocks and calendars
5 questions
Coding-decoding, series, patterns, cubes, dice and visual reasoning
110 questions
Communication, interpersonal skills and decision-making
10 questions
Counting, permutations, combinations and probability
1 questions
Directions, blood relations and Venn diagrams
60 questions
General English: grammar, vocabulary and comprehension
20 questions
General Hindi: grammar, vocabulary, dialects and comprehension
25 questions
Geometry and mensuration
26 questions
Number system and basic algebra (divisibility, HCF/LCM, remainders, digits, equations)
196 questions
Percentages, profit and loss, discount, simple and compound interest
47 questions
Ratio, proportion, averages, mixtures and alligation
47 questions
Syllogisms, statements and conclusions, assumptions and arguments
89 questions
Time and work; pipes and cisterns
2 questions
Time, speed and distance; trains, boats and streams; races
48 questions
Attempt the questions
Newest papers first. Tap an option; the answer and the reason appear instantly.
Read the passage
The Juvenile Justice (Care and Protection of Children) Act, or the JJ Act, 2015 allows for the possibility for trying adolescents above 16 as adults if they are accused of committing a heinous offence. A heinous offence is one with a minimum punishment of seven years. Offences such as culpable homicide and causing death by negligence, which are common in drunken driving cases, are not heinous offences because they do not have a prescribed minimum punishment. The JJ Act, amended in 2021, now categorises an offence that has no minimum sentence, but has a maximum sentence of seven years or more as a serious offence which nonetheless, in the opinion of activists, does not merit the transfer of a case to the adult criminal justice system.
Which of the following statements is/are correct?
- 1. If an offence has no minimum prescribed punishment, it cannot be considered heinous as per the JJ Act, 2015.
- 2. As per the JJ Act, 2021, an offence for which there is a provision for a maximum sentence of seven years or more, but no minimum sentence, is to be considered a serious offence.
Select the answer using the code given below.
Answer (c) & explanation
Both statements are correct (c). Step 1: statement 1: the passage says a heinous offence has a minimum punishment of seven years, and gives culpable homicide as an example that is not heinous "because they do not have a prescribed minimum punishment". So an offence with no minimum cannot be heinous: correct. Step 2: statement 2 repeats the 2021 amendment: no minimum sentence plus a maximum of seven years or more = serious offence. Correct. Step 3: so options (a), (b) and (d) fail.
Tip: when a passage gives a definition plus an example, use both to test statements. The example (culpable homicide) confirms the rule in statement 1.
Answer as per the official UPSC answer key.
| List-I (Relationship category) | List-II (Communication type) |
|---|---|
| A. Between cricket captain and team members | 1. Informal and firm |
| B. Between judge and lawyers in court | 2. Informal and open-ended |
| C. Between Vice Chancellor and Deputy Registrar | 3. Formal and open-ended |
| D. Between peers and coworkers | 4. Formal and firm |
Match List-I with List-II and select the answer using the code given below the Lists :
Answer (b) & explanation
The match is A-1, B-4, C-3, D-2 (b). Step 1: a court is the most formal and binding setting, so judge and lawyers = formal and firm (B-4). Peers and coworkers talk freely and loosely = informal and open-ended (D-2). Step 2: a cricket captain is friendly with players, but his decision is final = informal and firm (A-1). Step 3: a Vice Chancellor and Deputy Registrar work through official channels but discuss matters = formal and open-ended (C-3). Options (a), (c) and (d) mismatch these.
Tip: in matching questions, fix the clearest pairs first (here court and peers). The rest often fall into place.
Answer as per the official UPSC answer key.
If 10m × 1000 × n = 7525 × 2532 × 3275, where n is not divisible by 10, then the value of m is
Answer (b) & explanation
m is 111 (b). Step 1: each 10 needs one 2 and one 5. Count the 5s: 75²⁵ = (3 × 5²)²⁵ = 3²⁵ × 5⁵⁰, and 25³² = 5⁶⁴. Total 5s = 50 + 64 = 114. Step 2: count the 2s: 32⁷⁵ = (2⁵)⁷⁵ = 2³⁷⁵. Far more than 114. Step 3: so the right side has exactly 114 factors of 10 (n has no more, since n is not divisible by 10). The left side has 10ᵐ × 1000 = 10^(m + 3). So m + 3 = 114 and m = 111. Options (a), (c) and (d) fail.
Tip: the number of 10s equals the smaller count of 2s and 5s. Do not forget the extra 10s hidden in 1000.
remember the 1000 on the left: it already holds 103.
Answer as per the official UPSC answer key.
Seven cubes are identical in shape. Out of these, the weight of each of the six cubes is equal and the weight of the remaining cube is less than the weight of any other cube. A balance is used to identify the lightest cube. What is the minimum number of attempts required to distinguish the odd cube with certainty?
Answer (a) & explanation
Two weighings are enough (a). Step 1: put 3 cubes against 3, keeping one aside. If they balance, the cube kept aside is the light one: done in one weighing. Step 2: if one side is lighter, the odd cube is among those three. Weigh 1 against 1 of them. Step 3: the lighter pan holds the odd cube; if they balance, it is the third cube. So 2 weighings always work. One weighing (d) cannot cover all cases. Options (b) and (c) use more than needed.
Tip: each weighing has three outcomes (left, right, balance), so split into three groups. With n weighings you can find a light coin among up to 3ⁿ coins.
one weighing can only split the cubes into three groups (left, right, aside), so 7 cubes need at least two.
Answer as per the official UPSC answer key.
Suppose x, y and z are variables taking positive real numbers as their possible values. It is given that y is directly proportional to x2 and x is inversely proportional to z. For z = 7/25, the values of x and y are 5 and 50, respectively. If y = 98, what is z equal to?
Answer (b) & explanation
z equals 1/5 (b). Step 1: y is directly proportional to x², so y = k × x². With x = 5 and y = 50: 50 = k × 25, so k = 2. Step 2: y = 98 means 2x² = 98, so x² = 49 and x = 7. Step 3: x is inversely proportional to z, so x × z stays the same. At the start: 5 × 7/25 = 7/5. Now 7 × z = 7/5, so z = 1/5. Options (a), (c) and (d) fail.
Tip: "directly proportional" means the ratio stays fixed; "inversely proportional" means the product stays fixed. Find the constant first, then use it.
Answer as per the official UPSC answer key.
Read the passage
Was it the sun-dappled ambience, the strawberries and cream, the frustration of Flavio Cobolli’s unforced errors against Serbian Novak Djokovic on Centre Court or simply the crushing weight of being a 64-year-old man in the third act of a very public life? Whatever the reason, Hugh Grant, the actor, deserves empathy. There he was, in the Royal Box at Wimbledon, flanked by Britain’s well-dressed and well-rested spectators, watching the men’s singles quarterfinals, when the actor did something quietly radical : head at a tilt, eyes closed, utterly unbothered, he took a nap. So praise be to Grant for serving up an unexpected ace. In that small, delicious moment, he didn’t merely catch forty winks, he made an elegant case for surrender. Not to laziness, but to limits. To the body’s quiet wisdom over society’s relentless performance metrics. Wimbledon had its tennis. The perpetually sleep-deprived discovered a leading man, not of action, but of rest.
Which of the following statements is/are correct?
- 1. Hugh Grant was watching, from the Royal Box, the men’s semifinal match on Centre Court between Flavio Cobolli and Novak Djokovic.
- 2. The phrase ‘unexpected ace’ in the context uses a term from the game of tennis to highlight Hugh Grant’s somewhat uncharacteristic act of catching ‘forty winks’; an act that is viewed with opprobrium.
- 3. Grant subjects the demands of society to the wisdom of his body.
Select the answer using the code given below.
Answer (b) & explanation
Only statement 3 is correct (b). Step 1: statement 3 matches "the body's quiet wisdom over society's relentless performance metrics". Grant let his body's need win over social demands. Correct. Step 2: statement 1 says it was the semifinal. The passage says "men's singles quarterfinals". Wrong. Step 3: statement 2 rightly explains "ace" as a tennis term, but adds that the nap is viewed with "opprobrium" (disgrace). The writer praises it: "praise be to Grant". So 2 is wrong. Options (a), (c) and (d) fail.
Tip: a statement that is half right is still wrong. Check every part, especially the tone words like "opprobrium". The match was played on 9 July 2025.
Answer as per the official UPSC answer key.
How many words can one form by shuffling the letters of the word QUEUE, if Q is always followed by U? The words thus formed need not necessarily have any meaning.
Answer (d) & explanation
12 words can be formed (d). Step 1: Q must always be followed by U, so tie them together as one block, QU. Step 2: the letters of QUEUE are Q, U, E, U, E. After making the block, we have QU, U, E, E: four items. Step 3: four items can be arranged in 4 × 3 × 2 × 1 = 24 ways. But the two Es are identical, so swapping them gives the same word: 24 ÷ 2 = 12. Options (a), (b) and (c) miss arrangements or divide wrongly.
Tip: "always together" means treat them as one block. Then divide by the factorial of each repeated letter's count.
don't halve again for the Us. One U is inside the block, so the two Us are no longer interchangeable items.
Answer as per the official UPSC answer key.
An explosion takes place at a certain distance from an army camp. As soon as the sensor in the camp receives the sound of the explosion, a drone starts flying towards the spot of explosion. The drone clicks a picture from the spot and the camp receives it at the same time. Immediately another drone starts flying to the spot and it also sends a picture as soon as it reaches the spot. The two pictures were received at 5:02 PM and 5:05 PM, respectively. If the speed of the drones is 30 m/s, at what time did the explosion take place? Assume that the speed of sound is 300 m/s.
Answer (c) & explanation
The explosion happened at 4:58:42 PM (c). Step 1: drone 2 left at 5:02 (when picture 1 arrived) and reached the spot at 5:05. So one flight takes 180 seconds, and the distance = 30 × 180 = 5400 m. Step 2: drone 1 also flew 180 seconds and reached at 5:02, so it left at 4:59:00, the moment the sound reached the camp. Step 3: sound took 5400 ÷ 300 = 18 seconds. So the explosion was at 4:59:00 − 18 s = 4:58:42 PM. Option (a) forgets the sound delay. Options (b) and (d) miscalculate.
Tip: work backwards one step at a time. Pictures arrive instantly, so only flight time and sound travel time matter.
don't stop at 4:59:00. That is when the sound reached the camp, not when the blast happened.
Answer as per the official UPSC answer key.
| List-I (Tool of communication) | List-II (Purpose) |
|---|---|
| A. Memorandum | 1. To record decisions |
| B. Flyer | 2. To inform confidentially |
| C. Bcc | 3. To intimate a directive |
| D. Minutes | 4. To disseminate non-targeted information |
Match List-I with List-II and select the answer using the code given below the Lists :
Answer (c) & explanation
The match is A-3, B-4, C-2, D-1 (c). Step 1: Minutes are the written record of a meeting, so they record decisions (D-1). Step 2: a memorandum (memo) is an internal office note that conveys an instruction, so it intimates a directive (A-3). Step 3: a flyer is handed out to anyone, so it spreads non-targeted information (B-4). Bcc (blind carbon copy) hides recipients from each other, so it informs confidentially (C-2). Options (a), (b) and (d) mismatch.
Tip: know basic office communication terms: memo, circular, minutes, notice and agenda. "Cc" shows all recipients; "Bcc" hides them.
Answer as per the official UPSC answer key.
The speed of a train T is 100 km per hour and the speed of a person P is 4 km per hour. T crosses P in 15 seconds, if P travels along the direction of motion of T. If P travels along the opposite direction of T, then in how much time does T cross P, in seconds, approximately?
Answer (c) & explanation
The train crosses him in about 13.85 seconds (c). Step 1: same direction: relative speed = 100 − 4 = 96 km/h. The train takes 15 seconds to pass him. Step 2: opposite direction: relative speed = 100 + 4 = 104 km/h. The train's length stays the same, so time falls in proportion. Step 3: time = 15 × 96 ÷ 104 = 1440 ÷ 104 ≈ 13.85 seconds. Options (a), (b) and (d) are close numbers from rounding or arithmetic slips.
Tip: when the distance (train length) is the same, time is inversely proportional to relative speed. No need to find the length itself.
Answer as per the official UPSC answer key.
Read the passage
Previous waves of customer-service technology, including email and those pesky voice menus, stoked concerns of job losses, only for them to fail to materialise. AI could yet prove different. And if it does, its effects may be salutary. Human agents could be freed up to spend more time on creative and rewarding tasks, like using feedback to make products and services better—and thereby spend less time listening to irate customers!
Which one among the following statements most appropriately reflects the point of view of the given passage?
Answer (c) & explanation
The view is that AI might raise the value of human work by moving people to more fulfilling tasks (c). Step 1: the writer's own view is in the last lines: AI's effects "may be salutary" (good). Step 2: human agents "could be freed up" for "creative and rewarding tasks", like using feedback to improve products. That is (c). Step 3: option (a), no work left for humans, is extreme. Options (b) and (d) only describe the background about earlier technology, not the writer's point of view.
Tip: separate background from the author's view. Words like "may be salutary" usually mark the author's own opinion.
Answer as per the official UPSC answer key.
Read the passage
India is starting to deploy AI for critical use cases such as weather forecasting, pest detection and control, and crop yield optimisation. However, penetration is limited to a small subset of tech-savvy farmers. In the US and in Europe, generative AI tools have started offering precision farming at scale, integrating large datasets to provide real-time agronomic insights. For at-scale integration and accessibility of AI tools in India, it would be helpful to develop Indian languages-based AI tools for smallholder farmers, partner with AgTechs to create affordable AI solutions, and disseminate AI-based advisory services through government programmes.
Which of the following assumptions is/are valid?
- 1. Agricultural productivity has marched ahead in the West because of the economies of scale facilitated by the adoption of AI tools.
- 2. Affordable AI tools rendered available in local languages can help AI-based solutions reach more and more small farmers.
- 3. Though penetration is as yet low, critical application areas deploying AI tools are already in use in India.
Select the answer using the code given below.
Answer (d) & explanation
Assumptions 2 and 3 are valid (d). Step 1: the passage suggests Indian-language AI tools, affordable solutions with AgTechs, and government advisory services to reach smallholders. This rests on assumption 2: affordable, local-language tools can reach more small farmers. Step 2: it opens by saying India is already using AI for weather forecasting, pest control and crop yields, though only among tech-savvy farmers. That is assumption 3. Step 3: assumption 1 says Western farm productivity rose because of AI and economies of scale. The passage only says AI tools "have started" offering precision farming there. So options (a), (b) and (c) fail.
Tip: reject cause-and-effect claims the passage does not make. "Started offering" is not "caused growth".
Answer as per the official UPSC answer key.
Read the passage
The process by which countries close their labour-productivity gap with the technology leader is based on convergence theory. The convergence model divides economic eras into three phases : the breakaway, the catch-up, and the fine-tuning phase. It also divides economic entities into two categories : the technology leaders and the technology followers. The process begins with the development of a new technology, such as scavenging three million years ago (MYA), hunting—one MYA, farming—12 thousand years ago, and industrial technology—a little more than 200 years ago. During the breakaway phase, the per capita income of the technology leaders (e.g., Western Europe and North America in the industrial era) rises, but is unchanged for the technology followers. In the catch-up phase, the followers adopt the new technology and close their per capita income gap with the technology leaders. In the fine-tuning phase, where participants try to extract the remaining benefits from an increasingly exhausted technology, leaders and followers have similar per capita incomes.
Which of the following conclusions are correct?
- 1. In the breakaway phase, economic progress is slow for the technology followers.
- 2. In the catch-up phase, leaders stagnate and followers, therefore, close the gap between them and the leaders.
- 3. In the fine-tuning phase, technology is exhausted, as it were, and both leaders and followers attempt to extract leftover benefits, leading to more or less similar per capita income levels.
- 4. Industrial technology followed scavenging, which preceded hunting, which itself was followed by farming.
Select the answer using the code given below.
Answer (a) & explanation
Conclusions 3 and 4 are correct (a). Step 1: conclusion 3 restates the fine-tuning phase: participants extract the remaining benefits from an "increasingly exhausted" technology, and leaders and followers have similar incomes. Correct. Step 2: conclusion 4 follows the timeline: scavenging (3 million years ago), hunting (1 million), farming (12,000 years) and industry (200 years). Correct. Step 3: conclusion 1 says followers' progress is "slow" in the breakaway phase; the passage says their income is "unchanged". Conclusion 2 says leaders stagnate in catch-up; the passage only says followers close the gap. So options (b), (c) and (d) fail.
Tip: "unchanged" is not "slow"; "followers catch up" does not mean "leaders stagnate". Match the exact word.
Answer as per the official UPSC answer key.
X, Y and Z jump forward 4', 6' and 5', respectively. At 8 AM, they all land on mark 199'. How many times will they all land on the same mark (need not be at the same moment) between mark 195' and 1000', if all of them cross mark 1000' by 9 AM?
Answer (d) & explanation
They land on a common mark 14 times (d). Step 1: all three are at 199' together. After that, they share a mark every LCM(4, 6, 5) = 60'. So common marks are 199, 259, 319, … Step 2: the largest common mark up to 1000' is 199 + 60k ≤ 1000, so k ≤ 13 (199 + 780 = 979). Step 3: k = 0 to 13 gives 14 marks. The mark before 199 would be 139', which is below 195', so it does not count. Options (a), (b) and (c) miss the starting mark or the end.
Tip: common points repeat at the LCM. Count from the first shared point, and include both ends when they fall inside the range.
199' itself counts. It lies between 195' and 1000'.
Answer as per the official UPSC answer key.
The digit in the unit place of the number 6129 × 7307 is
Answer (c) & explanation
The unit digit is 8 (c). Step 1: every power of 6 ends in 6 (6, 36, 216, …). Step 2: powers of 7 end in a cycle of four: 7, 9, 3, 1. Divide 307 by 4: remainder 3. So 7³⁰⁷ ends in the third digit of the cycle: 3. Step 3: 6 × 3 = 18, so the unit digit is 8. Options (a), (b) and (d) use the wrong place in the cycle.
Tip: digits 0, 1, 5 and 6 keep the same unit digit for every power. For others, find the cycle of four and use the remainder of the power divided by 4.
Answer as per the official UPSC answer key.
Which among the following actions would constitute the most appropriate directive(s) in resolving interpersonal conflict in an office with culturally diverse personnel?
- 1. Direct personnel to practise activities that are the cultural markers of diverse groups
- 2. Allow conflicts to resolve naturally over time to set an appropriate precedent of leadership
- 3. Encourage personnel to seek each other's perspectives
Select the answer using the code given below.
Answer (c) & explanation
Only action 3 is appropriate (c). Step 1: action 1, forcing staff to practise other groups' cultural customs, can make people uncomfortable or offended. Respect cannot be imposed. Step 2: action 2, letting conflicts resolve on their own, is not leadership. Unresolved conflict usually grows and hurts teamwork. Step 3: action 3, encouraging staff to seek each other's perspectives, builds understanding and respect, the root of resolving cultural conflict. So options (a), (b) and (d) fail.
Tip: in workplace-ethics questions, prefer options that build dialogue and empathy. Avoid options that force behaviour or ignore problems.
in decision items, an option that forces people or does nothing is rarely the best one.
Answer as per the official UPSC answer key.
For 1/3 < x < y < 2, which of the following statements is/are always correct?
- I. x + 1/x < y + 1/y
- II. √(1 + y2)/y < √(1 + x2)/x
Select the answer using the code given below.
Answer (b) & explanation
Only statement II is always correct (b). Step 1: statement I: t + 1/t falls until t = 1, then rises. So it is not always increasing in this range. Test x = 1/2, y = 1: x + 1/x = 2.5, y + 1/y = 2. Here 2.5 is not less than 2, so I fails. Step 2: statement II: √(1 + y²)/y = √(1/y² + 1). As y grows, 1/y² shrinks, so this value gets smaller. Since x < y, the y-value is always smaller than the x-value. II always holds. Step 3: options (a), (c) and (d) fail.
Tip: "always correct" needs to hold for every case; one counter-example kills it. Rewrite expressions to see if they rise or fall.
the range crosses 1, where t + 1/t turns around. "Always" fails with one counter-example.
Answer as per the official UPSC answer key.
Read the passage
Previous waves of customer-service technology, including email and those pesky voice menus, stoked concerns of job losses, only for them to fail to materialise. AI could yet prove different. And if it does, its effects may be salutary. Human agents could be freed up to spend more time on creative and rewarding tasks, like using feedback to make products and services better—and thereby spend less time listening to irate customers!
Which of the following conclusions, made on the basis of the given passage, is/are correct?
- 1. The advent of new customer-service technology had invariably sparked fears about job losses.
- 2. Often it is found that instead of job losses, alternative channels for employee engagement are discovered while certain tasks are replaced by technology.
- 3. The advent of technology inevitably leads to stressful outcomes.
Select the answer using the code given below.
Answer (d) & explanation
Conclusions 1 and 2 are correct (d). Step 1: the passage says earlier waves like email and voice menus "stoked concerns of job losses". So new customer-service technology has sparked such fears (1). Step 2: those losses "failed to materialise", and AI may free humans for creative, rewarding work. So technology often redirects people rather than replacing them (2). Step 3: conclusion 3 says technology inevitably leads to stress. The passage expects salutary effects and less time with irate customers, the opposite. So options (a), (b) and (c) fail.
Tip: "inevitably" is a strong word; check that the passage supports it fully. Here it says the reverse.
Answer as per the official UPSC answer key.
Read the passage
India is starting to deploy AI for critical use cases such as weather forecasting, pest detection and control, and crop yield optimisation. However, penetration is limited to a small subset of tech-savvy farmers. In the US and in Europe, generative AI tools have started offering precision farming at scale, integrating large datasets to provide real-time agronomic insights. For at-scale integration and accessibility of AI tools in India, it would be helpful to develop Indian languages-based AI tools for smallholder farmers, partner with AgTechs to create affordable AI solutions, and disseminate AI-based advisory services through government programmes.
Which of the following statements is/are not correct?
- 1. Tech-savvy farmers will drive the AgTech companies of the future.
- 2. The development of advisory services by the government programmes for the use of AI tools in agriculture would be helpful.
- 3. In the US and Europe, AI tools have replaced traditional agricultural practices.
- 4. The integration of large datasets for use in real-time agronomic analysis is already a reality.
Select the answer using the code given below.
Answer (a) & explanation
Statements 1 and 3 are not correct (a). Step 1: statement 1 says tech-savvy farmers will drive AgTech companies. The passage only says AI use is limited to such farmers; it never says they will drive companies. Not correct. Step 2: statement 3 says AI has replaced traditional farming in the US and Europe. The passage says AI tools have "started offering" precision farming, not replaced old methods. Not correct. Step 3: statement 2 matches the suggestion of government advisory services, and statement 4 matches "integrating large datasets to provide real-time agronomic insights" already happening in the West. So both are correct, and options (b), (c) and (d) fail.
Tip: in "not correct" questions, mark each statement true or false, then pick the false ones.
Answer as per the official UPSC answer key.
Read the passage
The process by which countries close their labour-productivity gap with the technology leader is based on convergence theory. The convergence model divides economic eras into three phases : the breakaway, the catch-up, and the fine-tuning phase. It also divides economic entities into two categories : the technology leaders and the technology followers. The process begins with the development of a new technology, such as scavenging three million years ago (MYA), hunting—one MYA, farming—12 thousand years ago, and industrial technology—a little more than 200 years ago. During the breakaway phase, the per capita income of the technology leaders (e.g., Western Europe and North America in the industrial era) rises, but is unchanged for the technology followers. In the catch-up phase, the followers adopt the new technology and close their per capita income gap with the technology leaders. In the fine-tuning phase, where participants try to extract the remaining benefits from an increasingly exhausted technology, leaders and followers have similar per capita incomes.
Which of the following statements is/are correct?
- 1. The convergence model divides nations into three phases of economic progress.
- 2. At the heart of the convergence theory is the closing of the gap between labour and productivity.
- 3. Technology leaders typically have arrived earlier at different economic eras.
- 4. The time period covered by the convergence theory presented herein encompasses, as mentioned, 4012200 years.
Select the answer using the code given below.
Answer (b) & explanation
Statements 2 and 3 are correct (b), as per UPSC's key. Step 1: statement 2: the opening line says convergence is how countries close their labour-productivity gap with the leader. UPSC reads this as the heart of the theory. Step 2: statement 3: in the breakaway phase, leaders (such as Western Europe and North America) gain first, so leaders arrive earlier at new eras. Correct. Step 3: statement 1 says the model divides nations into three phases; it divides economic eras into phases and entities into two categories. Statement 4 gives a wrong total period; the process begins about 3 million years ago. So options (a), (c) and (d) fail.
Tip: check what is being divided: eras into phases, entities into leaders and followers. Mixing them is the trap.
Answer as per the official UPSC answer key.