You are presented with the question "When does a gas's density decrease?" and the following answer choices: 
- Time and energy
 - cool off
 - Dehydration
 - air cools
 - It becomes dormant
 - Evaporation
 - Dilution
 - When it's heated

Now knowing that if gas is heated then that gas will expand and if a material is heated, it expands and the density decreases, choose the best answer.


 

        When it's heated 