Answer:
Temperature decreases because fewer air molecules allow the air mass to expand.
Explanation:
Temperature of air mass decreases as it rises . It is so because at upper strata
of atmosphere , air is sparse and therefore air molecules there is relatively less . It results in lower pressure around air mass going up . This results in expansion of gas . Molecules have to do work against mutual attractive force for expansion so their energy becomes less . This cools down the air.