Question 34

They are made largely of hydrogen and helium.

The giant outer planets in the solar system, known as gas giants, are primarily composed of hydrogen and helium, distinguishing them significantly from terrestrial planets like Earth, which are mainly composed of rock and metal.

A) They are made largely of hydrogen and helium.

This option is correct as it accurately describes the composition of the giant outer planets, such as Jupiter and Saturn. These planets are predominantly made of gaseous materials, particularly hydrogen and helium, which is a fundamental characteristic that sets them apart from Earth.

B) They are extremely dense.

This option is incorrect because, while Earth is relatively dense due to its rocky composition, the giant outer planets have lower overall densities. They are less dense than Earth because their gaseous makeup contributes to a larger volume with less mass.

C) They lack orbiting moons.

This option is also incorrect, as the giant outer planets possess numerous moons. For instance, Jupiter and Saturn each have a significant number of moons orbiting them, which is contrary to the statement that they lack such satellites.

D) They tend to have a shorter period of revolution around the Sun.

This statement is incorrect as well. In fact, the giant outer planets have longer periods of revolution around the Sun compared to Earth. Their greater distance from the Sun results in longer orbital periods.

Conclusion

The correct answer is A, as the composition of hydrogen and helium is a defining trait of the giant outer planets, setting them apart from Earth’s rocky structure. All other options fail to accurately describe the characteristics of the giant outer planets, either presenting incorrect information about their density, moon count, or orbital periods.