Assertion : Increasing pressure on pure water decreases its freezing point.

Answer: (a) Both A and R are true and R is the correct explanation of A. Increasing the pressure on pure water affects its molecular structure, decreasing the space between molecules and thus increasing its density. This increased density and pressure influence the freezing point of water, resulting in the freezing point dropping as the pressure is increased. The maximum density of pure water occurs at a temperature of 273 K.