What happens to propane when it is heated?

When propane is heated, it undergoes a physical change that causes it to expand. This expansion is due to the increase in temperature leading to an increase in the kinetic energy of the propane molecules. As the molecules gain energy, they move more vigorously and tend to occupy more space, resulting in an increase in volume.

In the context of gases, when the temperature rises, the pressure and volume relationship defined by Charles's Law indicates that if the pressure is constant, the volume of a gas will increase along with temperature. This principle applies to propane and other gases, making the option of expansion the most accurate response.

The other scenarios presented—shrinking, evaporating, and solidifying—do not correctly depict the response of propane in a heated state. Propane can evaporate if it were in liquid form and heated to a point where it changes to gas, but the emphasis in this question is on the condition of being heated and the direct physical response, which is expansion. Solidifying would imply a decrease in temperature, which is opposite to the heating process.