Question

matter states and molecular density according to this diagram, as matter moves from solid, to liquid, to gas, molecules tend to... become greater in number. become less compacted. grow fewer in number. become more crowded.

Explanation:

In solids, molecules are closely - packed. In liquids, they are less closely - packed than in solids. In gases, molecules are far apart. So as matter moves from solid to liquid to gas, molecules become less compacted. The number of molecules remains the same during a phase change (assuming no chemical reaction or addition/removal of matter).

Answer:

become less compacted.