Question

The gases become denser at

Answer 1

In general, liquids are denser than gases; solids are denser than liquids. ... Liquid is more denser than gas. Although some say that on adding pressure on gas its density will increase and will become more than the liquid. But on pressure the gas will get compressed to liquid and its not gas anymore.

Answer 2

At low temperature evaporation is less, so the moisture content present in the air remain unaltered and hence exerts high pressure
Thus the gases become denser at low temperature and exerts high pressure