Practice Astronomy MCQs for Join Pak Navy: Initial Academic Test Everyday Science — topic-wise sets with solved answers.
Q1. Which is the brightest planet in the solar system?
Answer: Venus
Explanation: Venus is the brightest planet as seen from Earth due to its thick, highly reflective cloud cover that reflects about 70% of sunlight.
Q2. In a typical H-R diagram, stars are graphed by which two characteristics?
Answer: Temperature and Luminosity
Explanation: The Hertzsprung-Russell (H-R) diagram plots stars according to their luminosity (absolute brightness) on the y-axis and surface temperature (spectral class) on the x-axis.
Q3. How many planets are in our solar system:
Answer: 8
Explanation: Since Pluto was reclassified as a dwarf planet by the IAU in 2006, our solar system officially has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Q4. Which gas in Chlorofluorocarbons damages the ozone layer most:
Answer: Chlorine
Explanation: In CFCs, chlorine atoms are the primary ozone-depleting agents; a single chlorine atom can catalytically destroy thousands of ozone molecules in the stratosphere.
Q5. The ozone layer is at a height of ____ kilometers from the surface of the Earth.
Answer: 20 to 30
Explanation: The ozone layer is concentrated in the stratosphere at altitudes of approximately 20 to 30 kilometers above Earth's surface, where it absorbs harmful UV-B and UV-C radiation.
Q6. Phases of the moon occur because:
Answer: we can see only that part of the moon which reflects sunlight towards us.
Explanation: we can see only that part of the moon which reflects sunlight towards us. is the scientifically accurate choice. The concept tested here is core everyday science for MDCAT, ECAT, and general ability papers.
Q7. What is the brightest planet in the solar system?
Answer: Venus
Explanation: Venus is the brightest object in the night sky after the Moon due to its highly reflective cloud cover (albedo ~0.7) and relatively close proximity to Earth.
Q8. How long does it take for the Moon to orbit the Earth once (sidereal period)?
Answer: 27.3 days
Explanation: The Moon completes one orbit around Earth in 27.3 days (sidereal period), which is the time measured relative to distant stars rather than relative to the Sun.
Q9. The fastest-rotating planet is ____.
Answer: Jupiter
Explanation: Jupiter is the scientifically accurate choice. The concept tested here is core everyday science for MDCAT, ECAT, and general ability papers.
Q10. How many main layers does Earth's atmosphere have?
Answer: 5
Explanation: Earth's atmosphere is divided into five main layers based on temperature gradients: troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
Q11. About fifty percent of the Earth's crust, including the waters on the Earth and the atmosphere, is:
Answer: Oxygen
Explanation: Oxygen is the scientifically accurate choice. The concept tested here is core everyday science for MDCAT, ECAT, and general ability papers.
Q12. The approximate age of the Moon is ______.
Answer: 4.51 billion years
Explanation: Radiometric dating of lunar rocks and meteorites places the Moon's formation at approximately 4.51 billion years ago, shortly after the formation of the Solar System.
Q13. A lake starts freezing because of the cold atmosphere. It will first freeze:
Answer: At the top surface
Explanation: Water has maximum density at 4°C; as surface water cools below this, it becomes less dense and stays at the top, so ice forms first at the surface of a lake.
Q14. Which of the following planets has the longest day?
Answer: Venus
Explanation: Venus has the longest sidereal day in our solar system at about 243 Earth days, and uniquely rotates retrograde (opposite to its orbital direction).
Q15. Which of the following planets has the smallest diameter?
Answer: Mercury
Explanation: Among the eight planets, Mercury has the smallest diameter at approximately 4,879 km; Pluto, now classified as a dwarf planet, is not counted.
Q16. What is the closest planet to Earth?
Answer: Venus
Explanation: Venus is the scientifically accurate choice. The concept tested here is core everyday science for MDCAT, ECAT, and general ability papers.
Q17. The distance between the Earth and the Sun is smallest in the month of _____.
Answer: January
Explanation: Earth reaches perihelion (closest point to the Sun, ~147.1 million km) in early January, because Earth's elliptical orbit brings it nearest the Sun during the Northern Hemisphere winter.
Q18. What is the approximate mass of the Sun?
Answer: 2.0 x 10³⁰ kg
Explanation: The Sun's mass is approximately 1.989 × 10³⁰ kg, commonly rounded to 2.0 × 10³⁰ kg, and it contains about 99.86% of the total mass of the Solar System.
Q19. The time taken for sunlight to reach the Earth is ____ min ____ sec.
Answer: 8 mins 20 sec
Explanation: 8 mins 20 sec is the scientifically accurate choice. The concept tested here is core everyday science for MDCAT, ECAT, and general ability papers.
Q20. Which star is known as the Constant Star?
Answer: North Star
Explanation: Polaris (the North Star) is called the Constant Star because it remains nearly stationary in the night sky, always pointing north, while other stars appear to rotate around it.
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