A liquid boils when its vapor pressure equals the external pressure. If the external atmospheric pressure on a liquid is decreased, what happens to its boiling point?
Correct: B
Boiling is the process where a liquid changes into a vapor throughout the bulk of the liquid, not just at the surface. This occurs when the vapor pressure of the liquid becomes equal to the external pressure acting on the liquid's surface. If the external pressure (e.g., atmospheric pressure) is decreased, the liquid needs to achieve a lower vapor pressure to start boiling. Liquids produce lower vapor pressures at lower temperatures. Therefore, decreasing the external pressure lowers the boiling point of the liquid. A common example is water boiling at a lower temperature at high altitudes where atmospheric pressure is lower.