What happens to a gas when it is heated?

When a gas is heated, its molecules gain kinetic energy and move more rapidly. This increase in kinetic energy causes the molecules to collide with each other and with the walls of the container more forcefully and frequently. Because of this increased movement, the gas occupies a larger volume, leading to the expansion of the gas.

The ideal gas laws, specifically Charles's Law, show the relationship between temperature and volume: as the temperature of a gas increases, so does its volume, provided the pressure remains constant. This physical behavior of gases differentiates them from solids and liquids, which generally contract upon heating due to increased molecular interaction.

Thus, the correct understanding is that heating a gas results in expansion, confirming the accuracy of the selected answer.