Why do solids expand less than liquids?

The correct choice emphasizes that solids are closer together than liquids. In solids, the particles are tightly packed in a fixed arrangement, which means that they do not have much room to move. When temperature increases, the particles in solids vibrate more, but because they are so closely arranged, their ability to move farther apart and expand is limited.

In contrast, liquids have particles that are still in close proximity but are not held in fixed positions. They can slide past each other and have more freedom of movement, which allows liquids to expand more significantly when they are heated. The greater spacing between particles in liquids facilitates a larger expansion compared to solids when subjected to temperature changes.

This fundamental difference in particle arrangement and spacing accounts for the relative expansion of solids and liquids when temperature variations are introduced.