$(a)$ Give an example where a change in physical state occurs due to a change in pressure.
$(b)$ State two factors that determine the rate of diffusion of a liquid in another liquid.

(N/A) Liquefaction of gases,such as the compression of $LPG$ (Liquefied Petroleum Gas) into cylinders.
$(b)$ The two factors determining the rate of diffusion are:
$(i)$ Temperature: The rate of diffusion increases with an increase in temperature because the kinetic energy of the particles increases.
$(ii)$ Concentration/Density: The rate of diffusion decreases as the concentration or density of the liquid increases.