All Free Everyday Science MCQs with Answers

621. Which of the following layers make radio transmission possible?

• A. Troposphere
• B. Ionosphere
• C. Mesosphere
• D. Stratosphere
• E. None of these

Explanation: The ionosphere contains charged particles that can reflect or refract certain radio waves back toward Earth, allowing signals to travel beyond the horizon. The lower atmospheric layers do not provide this main long-distance effect.

622. Hygrometer is used for measuring the ____________?

• A. Speed of sound
• B. Density of milk
• C. Humidity of air
• D. Specific gravity of liquids
• E. None of these

Explanation: A hygrometer measures the moisture content, or relative humidity, of air. Instruments measuring pressure, density or specific gravity serve different purposes.

623. One of the main function of the earth's ozone layer is to ?

• A. Prevent global warming
• B. Filter out ultraviolet rays
• C. Absorb pollution
• D. All of the above

Explanation: Stratospheric ozone absorbs much of the Sun’s harmful ultraviolet radiation, especially UV-B and UV-C. It is not correctly described as a general pollution absorber or a direct preventer of global warming.

624. Human population growth is greatest in developing countries because ?

• A. the birth rate is high in developing countries
• B. the death rate is high in developing countries.
• C. much of the population has already reached the child bearing age.
• D. most of the world's population lives in industrialized countries.Trying Interactive Physics Simulation Software

Explanation: Population growth is greatest where birth rates remain high while death rates have fallen because of improved sanitation, medicine and food supply. A large young population can further increase growth, but high birth rate is the main general reason given here.

625. One of the countries through which equator passes is___________?

• A. Kenya
• B. Malaysia
• C. Malta
• D. Pakistan

Explanation: The equator crosses Kenya in East Africa, as well as countries such as Ecuador, Brazil and Indonesia. Malaysia, Malta and Pakistan lie north of the equator.

626. In night, when photosynthesis is stopped, plants__________?

• A. take in Carbon Dioxide
• B. give off Oxygen
• C. give off Carbon Dioxide
• D. None of these

Explanation: Photosynthesis stops or greatly decreases in darkness, but respiration continues in plant cells. Respiration uses oxygen and releases carbon dioxide, so plants give off carbon dioxide at night.

627. About 50% of the Earth's crust, including the waters on the Earth and atmosphere, is?

• A. Oxygen
• B. Cabon Dioxide
• C. Silicon
• D. Clay

Explanation: Oxygen forms about 46% of the Earth's crust by mass, making it the most abundant crustal element. The figure is often rounded to about 50%, while carbon dioxide and clay are not elemental components in this sense.

628. Acid rain is mainly caused by emissions of __________ in the atmosphere?

• A. Sulfur Dioxide and Potassium Nitrate
• B. Sulfur and Charcoal
• C. Nitrogen Oxide and Potassium Nitrate
• D. Sulfur Dioxide and Nitrogen Oxide

Explanation: Sulfur dioxide and nitrogen oxides react with atmospheric moisture to form sulfuric and nitric acids, which fall as acid rain. Potassium nitrate is not a principal atmospheric emission responsible for this process.

629. In general, wind speed of 10 -13 kph caused_______?

• A. minor or no damage
• B. considerable damage
• C. severe damage
• D. extreme damage

Explanation: A wind speed of 10 to 13 kph is only a gentle breeze on the Beaufort scale, so it generally causes minor or no damage. Considerable or severe damage requires much stronger winds.

630. Water covers __________ of the Earth's surface?

• A. 61%
• B. 67%
• C. 71%
• D. 76%Biological Sciences

Explanation: Water covers about 71% of Earth's surface, while land covers roughly 29%. Most of this water is in the oceans.