Explain Why does cool air sink and warm air rise in the atmosphere?

Cold air or cool air is more dense than hot/warm air, because of this. Warm air 'rises' and cold air 'sinks'. The cold air molecules are closer packed together than the warm air molecules. And the result of this is that warm air is less dense meaning also more apart which is why it rises.

Explanation:

answer; the tunica intima also called tunica interna, consists of elastic fibers,connective tissue and smooth muscle cells;