Question

The warm air is ____________ than cold air.

Answer 1

As a first step, you could read and understand the question well. You could think of all possible points related to warm air. That is, for example, on heating air, what are the parameters that change, etc. On understanding this point you could easily answer the question.

Complete step by step answer:
Let us recall that air is a mixture of various gases. Take for instance our atmosphere has 78% of Nitrogen, 21% oxygen along with a minute amount of carbon dioxide, hydrogen as well as neon. On heating up air, the molecules that comprise the air will gain high energy and hence will start moving which further results in the increase of distance between the air molecules.
On dividing mass of the gas by its volume, we get the density of a particular gas. That is, we could say that density would be inversely proportional to volume for a given gas.
On increasing the temperature by heating the air, we have greater distance between molecules of air and hence greater volume and thereby lesser density. So, we could say that the less dense air would float over the denser air.
So, we could make this conclusion: ‘The warm air is lighter than cold air.’

Note: On heating the air, the mass would still remain the same as only the volume is being increased. So, at constant mass, density of the air would only have an inverse relation with volume. Take for example a hot air balloon, on being heated up it starts floating which proves our point.