All Free Everyday Science MCQs with Answers

681. What is the percentage of salt water on earth surface?

• A. 93%
• B. 95%
• C. 97%
• D. 76%

Explanation: About 97% of Earth’s water is salt water, found mainly in the oceans and seas. Only roughly 3% is fresh water.

682. The maximum risk to air travel is from?

• A. Clouds
• B. Rainfall
• C. Fogs
• D. Strong Winds

Explanation: Fog is especially hazardous to air travel because it sharply reduces visibility during take-off, landing, and ground movement. Strong winds can also be dangerous, but fog is the standard answer for visibility-related aviation risk.

683. Mercury is the closest planet to the Sun, but Venus is hotter than Mercury because of its_________?

• A. Pressure
• B. axis
• C. atmosphere
• D. surface

Explanation: Venus has a very dense carbon-dioxide atmosphere that produces an intense greenhouse effect and traps heat. Mercury has almost no atmosphere, so it cannot retain heat as effectively.

684. Which part of the atmosphere are you breathing right now?

• A. Bathysphere
• B. Stratosphere
• C. Troposphere
• D. Lonosphere

Explanation: Humans live and breathe in the troposphere, the lowest atmospheric layer where most air, water vapour, clouds, and weather occur. The stratosphere lies above it.

685. Our atmosphere consists of__________ CO2?

• A. 0.03 to 0.04% CO2
• B. 0.3 to 0.4% CO2
• C. 3 to 4% CO2
• D. None of these

Explanation: Carbon dioxide forms roughly 0.04% of the atmosphere today, commonly stated in older texts as 0.03 to 0.04%. The other ranges are far too high for atmospheric CO₂.

686. Our atmosphere consists of___________ Oxygen approximately?

• A. 11% Oxygen approximately
• B. 21% Oxygen approximately
• C. 31% Oxygen approximately
• D. None of these

Explanation: Oxygen makes up approximately 21% of dry air by volume. Nitrogen is the larger component at about 78%.

687. Our atmosphere comprises of __________ Nitrogen?

• A. 38% Nitrogen
• B. 58% Nitrogen
• C. 78% Nitrogen
• D. None of these

Explanation: Nitrogen constitutes approximately 78% of Earth’s dry atmosphere. Most of the remaining air is oxygen, with small amounts of other gases.

688. Which of the following is a volcanic plateau?

• A. Antrum Plateau
• B. Brazilian Plateau
• C. Anatolia Plateau
• D. Tibetan Palteau

Explanation: The Antrim Plateau in Northern Ireland is a volcanic plateau formed mainly from extensive basalt lava flows. “Antrum” is a misspelling of Antrim, but it clearly identifies the intended option.

689. ________ is an instrument used in determining the directions of movement of clouds.

• A. Nephoscope
• B. Stethoscope
• C. Metroscope
• D. None of the above

Explanation: A nephoscope is used to observe and determine the direction and movement of clouds. A stethoscope is a medical instrument for listening to internal body sounds.

690. _________ means a line on a map connecting points having the same atmospheric pressure at a given time or on average over a given period.

• A. Isobar
• B. Isobath
• C. Isohel
• D. Isohyet

Explanation: An isobar joins points with equal atmospheric pressure. By contrast, an isobath shows equal water depth, an isohel equal sunshine, and an isohyet equal rainfall.