Which is lighter, water or liquid propane?

Liquid propane is indeed lighter than water. This is primarily due to the difference in density between the two substances. Water has a density of approximately 1 gram per cubic centimeter at room temperature, while liquid propane has a density of about 0.5 grams per cubic centimeter.

Because of this lower density, when equal volumes of both substances are compared, liquid propane will weigh less than the same volume of water. This characteristic is significant in practical applications, such as fuel storage and transport, where understanding the buoyancy or weight differences can influence design and handling considerations.

The other answer choices do not hold true in the context of comparing the densities of water and liquid propane. The notion that both are equal in weight is incorrect, and while temperature can affect density slightly for both substances, the fundamental comparison remains valid regardless of common temperature ranges.