Question

When air is heated it expands and ________. when air is heated it expands and ________. contracts burns lowers its pressure sinks explodes?

Answer 1

When air is heated it expands and sinks. 

When air is heated it expands and becomes lighter and then it rises, but the cold air from the surrounding rushes in to fill the gap. It cools the hot air and then it becomes denser and heavier, so it eventually sinks down.