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Science — UPSC Prelims MCQs

1,131+ practice questions across 14 chapters, including 314+ previous year questions— each with option-by-option explanations.

Chapters in Science

Sample Science questions

A preview of the kind of MCQs you'll practise — with the correct answer and explanation.

Q1ScienceDisease, Immunity and Public Health

With reference to the immune system, consider the following statements: 1. T-cells are produced in the bone marrow and mature in the thymus. 2. B-cells produce antibodies when activated by an antigen. 3. Both T-cells and B-cells are part of innate immunity. Which of the statements given above is/are correct?

  • A1 and 2 onlyCorrect
  • B2 and 3 only
  • C1 only
  • D1, 2 and 3

Explanation

Correct. T-cells originate in bone marrow and mature in the thymus, and B-cells produce antibodies; both belong to adaptive (not innate) immunity.

Why the other options are incorrect
Option B

Statement 3 is incorrect; T-cells and B-cells are components of adaptive immunity, not innate immunity.

Option C

Statement 2 is also correct; activated B-cells differentiate into plasma cells that secrete antigen-specific antibodies.

Option D

Statement 3 is wrong; innate immunity involves physical barriers, phagocytes, and NK cells, while T and B lymphocytes mediate adaptive immunity.

Q2ScienceChemistry in Everyday LifePYQ 2015

With reference to 'fuel cells' in which hydrogen-rich fuel and oxygen are used to generate electricity, consider the following statements: 1. If pure hydrogen is used as a fuel, the fuel cell emits heat and water as by-products. 2. Fuel cells can be used for powering buildings and not for small devices like laptop computers. 3. Fuel cells produce electricity in the form of Alternating Current (AC). Which of the statements given above is/are correct?

  • A1 onlyCorrect
  • B2 and 3 only
  • C1 and 3 only
  • D1, 2 and 3

Explanation

Correct. When pure hydrogen reacts with oxygen in a fuel cell, the only by-products are heat and water. Fuel cells can power devices of all sizes (not just buildings), and they produce DC, not AC.

Why the other options are incorrect
Option B

Fuel cells produce Direct Current (DC), not AC, and they can power small devices like laptops, making both statements 2 and 3 wrong.

Option C

Fuel cells inherently generate DC electricity through electrochemical reactions; an inverter is needed if AC is required.

Option D

Statements 2 and 3 are both incorrect: fuel cells scale from portable devices to buildings, and they produce DC.

Q3SciencePhysics in Everyday Life

A concave mirror is commonly used in which of the following?

  • ARear-view mirrors of vehicles
  • BShaving mirrors and dentist's mirrorsCorrect
  • CStreet-light reflectors only
  • DPeriscopes

Explanation

Correct. Concave mirrors produce a magnified and upright image when the object is placed between the focus and the pole, making them ideal for shaving mirrors and dentist's mirrors where a larger view of close objects is needed.

Why the other options are incorrect
Option A

Rear-view mirrors are convex mirrors because they provide a wider field of view.

Option C

While concave reflectors can be used in some lighting, the most common everyday application is in personal grooming and dental examination.

Option D

Periscopes use plane mirrors (or prisms) to redirect light, not concave mirrors.

Q4ScienceSpace Science and Astronomy

Which of the following statements about the International Space Station (ISS) is/are correct? 1. It orbits the Earth in low Earth orbit at an altitude of approximately 400 km. 2. It takes about 90 minutes to complete one orbit around the Earth. 3. It is a joint project involving NASA, Roscosmos, JAXA, ESA and ISRO. Select the correct answer using the code given below:

  • A1 and 2 onlyCorrect
  • B2 and 3 only
  • C1 only
  • D1, 2 and 3

Explanation

Correct. The ISS orbits at ~400 km altitude and completes an orbit in about 90 minutes. ISRO is not a partner agency of the ISS project.

Why the other options are incorrect
Option B

Statement 3 is incorrect; the ISS partner agencies are NASA, Roscosmos, JAXA, ESA and CSA (Canadian Space Agency). ISRO is not a partner.

Option C

Statement 2 is also correct; the ISS completes about 15.5 orbits per day, meaning each orbit takes approximately 90 minutes.

Option D

Statement 3 is wrong; ISRO is not among the five partner agencies of the ISS.

Q5ScienceHuman Physiology

Consider the following statements: 1. The adrenal glands are located above each kidney. 2. The adrenal medulla secretes adrenaline and noradrenaline. 3. The adrenal cortex secretes insulin. Which of the statements given above is/are correct?

  • A1 and 2 onlyCorrect
  • B2 and 3 only
  • C1 only
  • D1, 2 and 3

Explanation

Correct. The adrenal glands sit atop the kidneys and the adrenal medulla secretes adrenaline and noradrenaline. The adrenal cortex secretes corticosteroids (cortisol, aldosterone), not insulin.

Why the other options are incorrect
Option B

Statement 3 is incorrect; insulin is secreted by the pancreas, not the adrenal cortex.

Option C

Statement 2 is also correct; the adrenal medulla does secrete catecholamines (adrenaline and noradrenaline).

Option D

Statement 3 is wrong; the adrenal cortex produces cortisol and aldosterone, while insulin comes from the pancreas.

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