What does vapor pressure indicate?

• A. How easily a substance will evaporate
• B. The amount of pressure required to condense a gas into a liquid
• C. The amount of force a gas exerts on a container
• D. Whether a gas will rise or fall when released into the atmosphere

Answer: (A)

Vapor pressure is the pressure exerted by the vapor in equilibrium with its liquid at a given temperature, and it shows how readily the liquid will evaporate. A higher vapor pressure means molecules escape into the vapor phase more easily, indicating greater volatility. This is why liquids with high vapor pressure can produce flammable vapors quickly, which is a key consideration in fire scenarios. The other ideas describe different concepts: the external pressure needed to condense a gas, the general pressure a gas exerts in a container, or whether a gas will rise or fall in air, none of which define how easily a liquid evaporates.