Assertion (A): The boiling point of water decreases as the altitude increases. Reason (R): The atmospheric pressure increases with altitude.

Assertion (A) is true. The boiling point of a liquid is the temperature at which its vapor pressure equals the surrounding atmospheric pressure. As altitude increases, the atmospheric pressure decreases. Therefore, at higher altitudes, water boils at a lower temperature because its vapor pressure reaches the lower atmospheric pressure at a lower temperature. Reason (R) is false. Atmospheric pressure decreases, not increases, with increasing altitude. This is because there is less air mass above a given point at higher altitudes, resulting in lower pressure exerted by the weight of the air column.