You will be given a definition of a task first, then some input of the task.
In this task, you are given a question and answer for that. The answer will fill in the blank or will complete the unfinished question. Your task is to provide an explanation based on the given question or fill-in-the-blank statement, and answer.

Question: If air warms, it becomes _____ dense. 
 Answer: less
Output:
Warm air is less dense than cool air, so it rises higher in the troposphere.