All Free Everyday Science MCQs with Answers

801. Which of the following is responsible for largest amount of oxygen on earth?

• A. Peat bogs
• B. Algae
• C. Trees
• D. None of these

Explanation: Marine algae and microscopic phytoplankton carry out enormous amounts of photosynthesis and produce roughly half of Earth’s oxygen. Trees contribute oxygen, but they are not the largest overall source.

802. Which of the following gases do plants and trees give out during photosynthesis?

• A. Hydrogen
• B. Nitrogen
• C. Oxygen
• D. Carbon dioxide

Explanation: During photosynthesis, plants use carbon dioxide and water to make glucose, releasing oxygen as a by-product. This oxygen enters the atmosphere through tiny pores in leaves.

803. In which part of the Plant does photosynthesis take place?

• A. Flowers
• B. Roots
• C. Stem
• D. Leaves

Explanation: Photosynthesis occurs mainly in the leaves because their green cells contain chlorophyll inside chloroplasts. Chlorophyll captures light energy to help convert water and carbon dioxide into food.

804. A group of elephants is called___________?

• A. ZEAL
• B. Herd
• C. MOB
• D. TOWER

Explanation: Elephants are social animals that live and move in groups called herds. “Tower” is a collective noun associated with giraffes, not elephants.

805. Air contains maximum amount of__________?

• A. oxygen
• B. nitrogen
• C. hydrogen
• D. carbon dioxide

Explanation: Dry air contains about 78% nitrogen, compared with about 21% oxygen. Hydrogen and carbon dioxide are present only in very small amounts.

806. Radon is___________?

• A. germon radio
• B. radio active gas
• C. artificial fibre
• D. an explosive

Explanation: Radon is a naturally occurring radioactive noble gas produced during the decay of uranium in rocks and soil. It can accumulate indoors and increase lung-cancer risk after prolonged exposure.

807. What Color does chlorophyll not absorb?

• A. Red
• B. Blue
• C. Green
• D. Yellow

Explanation: Chlorophyll absorbs mainly blue-violet and red light but reflects green light, which is why leaves appear green. Green is therefore the standard answer for the colour it does not effectively absorb.

808. For water purification, we use?

• A. Chlorine
• B. Bromine
• C. Plants
• D. Young man

Explanation: Chlorine is added to water to kill many disease-causing microorganisms during disinfection. Bromine can disinfect in special applications, but chlorine is the standard agent used in public water purification.

809. Air contains volume of carbon dioxide approximately?

• A. 3%
• B. 33%
• C. 0.3%
• D. 0.03%

Explanation: Traditional atmospheric composition tables give carbon dioxide as about 0.03% by volume, although the present value is slightly above 0.04%.

810. During a total solar eclipse there is most likely to be_____________?

• A. A decrease in the rate of photosynthesis
• B. An increase in the rate of photosynthesis
• C. A decrease in the rate of respiration
• D. No effect on either photosynthesis or respiration

Explanation: A total solar eclipse temporarily reduces sunlight, so the light-dependent reactions of photosynthesis slow down. Respiration does not stop, making decreased photosynthesis the best answer.