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Basic Science MCQs

Everyday science MCQs on physics, chemistry and biology basics, with short explanations, for competitive exams.

10 MCQsUpdated 27 October 2026

A quick-revision set of the science facts that appear in almost every general knowledge paper: SI units, the composition of the air, body temperature, photosynthesis, hardness of diamond and simple chemical formulas.

Use this topic as a warm-up before the more detailed science sets. If any answer here surprises you, follow it into the related topic, such as physics units or human health, for the full picture.

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  1. 1

    The SI unit of force is:

    Correct answer: C. Newton

    The newton (N) is the force that gives a 1 kg mass an acceleration of 1 m/s². It is named after Sir Isaac Newton.

    easy
  2. 2

    Which vitamin is produced in the human skin by sunlight?

    Correct answer: D. Vitamin D

    The skin makes Vitamin D when exposed to ultraviolet-B rays from sunlight. The body needs it to absorb calcium.

    easy
  3. 3

    The approximate speed of light in vacuum is:

    Correct answer: B. 3 × 10⁸ m/s

    Light travels at about 3 × 10⁸ m/s (exactly 299,792,458 m/s) in vacuum. 340 m/s is roughly the speed of sound in air.

    easy
  4. 4

    Which gas makes up the largest part of Earth's atmosphere?

    Correct answer: B. Nitrogen

    Nitrogen makes up about 78% of the atmosphere, oxygen about 21% and argon nearly 1%.

    easy
  5. 5

    The lightest gas is:

    Correct answer: B. Hydrogen

    Hydrogen is the lightest element and gas, with an atomic mass of about 1.

    easy
  6. 6

    Which organelle is known as the "powerhouse of the cell"?

    Correct answer: C. Mitochondria

    Mitochondria produce most of the cell's energy as ATP through cellular respiration.

    easy
  7. 7

    The normal temperature of the human body is about:

    Correct answer: B. 37 °C

    Normal body temperature is about 37 °C (98.6 °F), though it varies slightly between people and through the day.

    easy
  8. 8

    The hardest naturally occurring substance is:

    Correct answer: C. Diamond

    Diamond, a form of carbon, ranks 10 on the Mohs hardness scale. Graphite is also carbon but is soft.

    easy
  9. 9

    During photosynthesis, plants take in:

    Correct answer: C. Carbon dioxide

    Plants take in carbon dioxide and water and use sunlight to make glucose, releasing oxygen as a by-product.

    easy
  10. 10

    The chemical formula of common salt is:

    Correct answer: A. NaCl

    Common salt is sodium chloride (NaCl).

    easy