What kind of air moves downslope into a valley after sunset in mountainous areas? Land breeze?

The correct answer and the kind of air that moves downslope into a valley after sunset in mountain areas is cool air.

This phenomenon is also known as mountain breeze, and it occurs when mountains create moisture through the emision of oxygen and carbon. After sunset, the air in the mountain slopes gets cold. Then, due to the gravitational flow, these breezes and dense air flow down the mountain causing cold wind.