What do these two changes have in common? rain forming in a cloud water freezing into ice

They're both examples of matter changing states.

Explanation:

Clouds = vapor, then forming rain = liquid

water = liquid freezing into ice = solid

mountains

Explanation:

Hydrological system of earth is the hydrosphere. It consists of total amount of water present on earth. The water is present in the atmosphere in the gases form (water vapor). The water accumulates in the geosphere is the groundwater. Glaciers are the sources of water in the solid form of ice.

Mountains are not the part of hydrological system.