Which of the following types of planets are described as having a mostly rocky composition?

The type of planets that are primarily characterized by a mostly rocky composition are terrestrial planets. These planets, which include Earth, Mars, Venus, and Mercury, are composed mainly of solid materials like rock and metals. Their surfaces are also marked by geological features such as mountains, valleys, and craters, which reflect their rocky nature.

Terrestrial planets are found in the inner solar system, where temperatures are higher, allowing for the solidification of various minerals and metals. This contrasts with gas giants—like Jupiter and Saturn—which are composed largely of hydrogen, helium, and other gases, and do not have solid surfaces. Dwarf planets and meteoroids, although they can also have rocky elements, do not fit the description as precisely as terrestrial planets do.

Overall, the defining aspect of terrestrial planets is their rocky surfaces and solid composition, making them distinct within the classification of planets in our solar system.