Final answer:
Valley breezes occur at night, and mountain breezes occur in the day due to topographic effects resulting from the interaction between the land and air in different geographical areas.
Step-by-step explanation:
Valley breezes usually occur at night, and mountain breezes usually occur in the day. This is caused by topographic effects resulting from the interaction between the land and air in different geographical areas. During the day, the sun heats the land more than the surrounding air, causing the air to rise up the mountain slopes, creating mountain breezes. At night, the land cools down faster than the air, causing the air to flow down the slopes into the valleys, creating valley breezes.