Which property of alcohol allows it to evaporate before water during heating?

The correct understanding of why alcohol can evaporate before water during heating is tied to its boiling point. Alcohol, such as ethanol, has a lower boiling point than water, which means it transitions from a liquid to a gas at a lower temperature.

When a mixture of alcohol and water is heated, the alcohol will begin to evaporate as soon as the temperature reaches its boiling point, which typically occurs before the boiling point of water is reached. This property is utilized in processes like distillation, where alcohol can be separated from water based on their different boiling points.

Therefore, the lower boiling point of alcohol is the key factor that enables it to evaporate before water during heating.