Question

Why does hot air rises up when gravity pulls everything towards it? How does the density of air changes as we go up in the atmosphere?

Answer 1

Hot airs have low density then cold airs so here buoyancy force is acted on hot air in upward direction This the reason for hot air rises up.
As we go up in the atmosphere, air density decreases. Near the earth surface density of air is low compare to some metre height above the earth surface.Because the earth surface is hotter in summer day