Why does it get cooler the higher the elevation. Like in the mountains?

Question

Is it because oxygen is less ( less density of air ) in elevated places, like in the mountains? if yes why does that make it cooler?

Answer 1

the temp decreases as we go to higher elevation as the atmosphere gets heated when it comes in contact with the hot land and gets heated and rise and it the higher elevations get cooled as they no longer come in contact with as much as land in lower elevation

so they get cooler

i think this has nothing to do with oxygen as the only effect of less quantity of oxygen is that one finds it difficult (not as easy as)to breath in higher elevations

Answer 2

Because gases (like air) expand and cool as the pressure decreases (with incerasing altitude), and compress and warm as the pressure increases (with decreasing altitude).

The rate at which this occurs with height is called the lapse rate (of temperature).