Consider the following statements in case of terrestrial planets : I. Mercury, Venus, Earth and Mars are terrestrial planets having low densities as compared to other planets. II. They lie between the Sun and the belt of asteroids. III. Their lower gravity can hold the escaping gases. Which of the statements given above is/are correct?
- A.I and II
- B.II and III
- C.I and III
- D.II only
Correct answer
Explanation
The correct answer is D, II only. The four terrestrial planets do lie between the Sun and the asteroid belt, but they are dense, not light, and their weak gravity could not hold on to escaping gases.
Mercury, Venus, Earth and Mars are called terrestrial, or Earth-like, because they are made of rock and metal. That makes them the densest planets; the Earth, at about 5.5 g/cm³, is the densest of all. They formed close to the Sun, where it was too hot for gases to condense, and their smaller mass and lower gravity could not hold back the gases that escaped. The giant outer planets, Jupiter to Neptune, are mostly gas and far less dense.
A is wrong because statement I is false: terrestrial planets have high densities. B is wrong because statement III is false: lower gravity lets gases escape. C is wrong because both I and III are false.
Exam tip: inner planets rocky and dense, outer planets gaseous and light; the asteroid belt lies between Mars and Jupiter.
Practice Questions
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- B.2 and 4
- C.1 and 3 only
- D.1 only
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- B.J.J. Thomson
- C.Niels Bohr
- D.Albert Einstein
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