The correct answer is - Object Y.
The object marked with the letter Y is the object that is a gaseous giant. In fact, that is the planet of Uranus. This planet is much larger than the terrestrial planets. It is also a planet where the gases predominate, and it doesn't have crustal or any other solid parts.
Uranus is the third largest planet in our Solar System but the fourth by mass, and it is the seventh most distant planet from the star in our Solar System, the Sun. The planets orbit takes 84 years to complete, but the rotation on its axis is actually pretty fast, with only 17 hours and 14 minutes for one rotation.