Answer:
a. size and composition
Step-by-step explanation:
The inner planets differs from the outer planets mostly and mainly in terms of their sizes and composition.
Inner planets are also know as the terrestrial planets. They are the first four planets closest to the sun. They are mostly solids with rocky masses.
The outer planets are located beyond the asteroid belts. They are the last four planets before the Kuiper belt objects. These planets are also called Jovian planets predominantly made up of gases.
The inner planets are smaller compare to the outer planets in size.
The outer planets are gas giants and the inner planets are rocky masses.