The uppermost layer is the crust . It is thin and solid. The lithosphere is made up of the crust and upper mantle and is broken into plates which move independently of each other. Lithos from the Greek means stone which implies rigidity. The solid lithosphere can move on the plastic asthenosphere which means that the surface is continually reforming - it is active and dynamic.
Mercury shows no traces of active movement.
It has a large iron-nickel core, but evidently does not have a plastic layer for the crust to move around on. It is small and may not have been able to provide enough internal heat after initial cooling to generate movement. Venus similar density to Earth, heavy atmosphere prevents us from knowing much about planet. There is an ongoing debate about the thickness of the crust and the nature of the internal structure. Volcanically active as recent as 300 million years ago.