Correct Answer: Relax completely

Solution : The correct choice is the third option .

The idiom chill out is a casual expression that suggests taking it easy, calming down, or relaxing.

It is often used to advise someone to become less stressed, anxious, or agitated in a given situation. So, if someone tells you to chill out, they are suggesting that you should take a moment to unwind and not let stress or tension affect you.

Therefore, among the given options, the most appropriate meaning of the given idiomatic expression is relax completely.