Level 1
Earth Science MCQs set 3 for PPSC Sanitary Inspector (BS-11) Everyday Science — 20 solved questions.
Q1. Why does the ocean appear blue?
Answer: Because the sunlight falling on it is scattered
Explanation: The ocean appears blue primarily because water molecules selectively absorb longer wavelengths (red, orange) and scatter shorter wavelengths (blue) - Rayleigh scattering also contributes.
Q2. Light from the Sun travels a distance before it reaches the Earth of about:
Answer: 150 million km
Explanation: The average Earth-Sun distance is approximately 150 million km (1 Astronomical Unit); light traveling at 300,000 km/s takes about 500 seconds (8 min 20 s) to traverse this distance.
Q3. Which unit is used to measure the ozone layer?
Answer: Dobson
Explanation: The thickness of the ozone layer is measured in Dobson Units (DU), named after meteorologist G.M.B. Dobson.
Q4. Heat from the sun's rays to Earth is reduced by:
Answer: Ozone
Explanation: Ozone is the scientifically accurate choice. The concept tested here is core everyday science for MDCAT, ECAT, and general ability papers.
Q5. The point in the Earth's orbit when it is farthest from the Sun, occurring around July 4th, is called:
Answer: Aphelion
Explanation: Aphelion is the point in Earth's elliptical orbit where it is farthest from the Sun (~152 million km), occurring around July 4th each year.
Q6. Sunsets on Mars are:
Answer: Blue
Explanation: Fine dust particles suspended in Mars' thin atmosphere scatter shorter red wavelengths away from the sunset direction, leaving blue-grey hues near the sun at dusk.
Q7. An eclipse of the Sun occurs when:
Answer: The Moon is between the Sun and the Earth
Explanation: A solar eclipse occurs when the Moon passes directly between the Sun and Earth, blocking sunlight and casting the Moon's shadow on Earth's surface.
Q8. Why is Ozone important for mankind?
Answer: Protection from ultraviolet rays of the sun
Explanation: The ozone layer in the stratosphere absorbs most of the Sun's harmful ultraviolet (UV-B and UV-C) radiation, preventing it from reaching Earth's surface.
Q9. Who among the following discovered sunspots?
Answer: Galileo
Explanation: Galileo Galilei first observed and systematically studied sunspots using a telescope around 1610-1611, demonstrating that the Sun is not a perfect celestial body.
Q10. The distance of Mercury from the Sun is:
Answer: 57.9 million km
Explanation: 57.9 million km is the scientifically accurate choice. The concept tested here is core everyday science for MDCAT, ECAT, and general ability papers.
Q11. The coldest region in the atmosphere is the:
Answer: Mesopause
Explanation: Mesopause is the scientifically accurate choice. The concept tested here is core everyday science for MDCAT, ECAT, and general ability papers.
Q12. The zone of the atmosphere in which the ozone layer is present is the:
Answer: Stratosphere
Explanation: The ozone layer is concentrated in the stratosphere, approximately 15-35 km above Earth's surface, where it absorbs harmful ultraviolet radiation from the Sun.
Q13. Most of the ozone in the atmosphere is concentrated in the ______.
Answer: stratosphere
Explanation: The ozone layer is concentrated in the stratosphere at altitudes of about 15-35 km, where it shields Earth from harmful ultraviolet radiation.
Q14. The gases used by divers as an artificial atmosphere are helium and:
Answer: Oxygen
Explanation: Divers use a helium-oxygen (heliox) mixture because helium does not cause nitrogen narcosis at depth, making it far safer than breathing compressed air.
Q15. Light takes about ______ to reach Earth from the Sun?
Answer: 8 Minutes
Explanation: 8 Minutes is the scientifically accurate choice. The concept tested here is core everyday science for MDCAT, ECAT, and general ability papers.
Q16. Our Sun is classified as a ______.
Answer: Yellow Dwarf
Explanation: Yellow Dwarf is the scientifically accurate choice. The concept tested here is core everyday science for MDCAT, ECAT, and general ability papers.
Q17. The ozone layer protects life on Earth from what?
Answer: Ultraviolet rays
Explanation: The ozone layer in the stratosphere absorbs most of the Sun's harmful ultraviolet (UV) radiation, particularly UV-B and UV-C, preventing it from reaching Earth's surface.
Q18. Who propounded the theory that the Earth revolves round the Sun?
Answer: Copernicus
Explanation: Nicolaus Copernicus proposed the heliocentric model in his 1543 work "De revolutionibus orbium coelestium," placing the Sun at the centre of the solar system.
Q19. The intensity of an earthquake is measured with a:
Answer: Seismograph
Explanation: A seismograph (or seismometer) records ground motion caused by earthquakes; the Richter scale and moment magnitude scale use seismographic data to quantify earthquake intensity.
Q20. A year (orbital period) is the longest on which planet?
Answer: Neptune
Explanation: Neptune has the longest orbital period of all planets at approximately 165 Earth years, due to its vast distance from the Sun - about 30 AU away.