If gas is heated then that gas will expand, and if a material is heated, it expands and the density decreases. Given these facts, when does a gas's density decrease among the following options:
- Time and energy
 - cool off
 - Dehydration
 - air cools
 - It becomes dormant
 - Evaporation
 - Dilution
 - When it's heated


 

        When it's heated 