Explanation:

- Option 4: To calm down

- This is the correct meaning of the idiom. "To take a chill pill" means to relax or calm down, usually after being overly stressed, anxious, or upset. People often use this phrase to suggest someone should not take things too seriously.

- Option 1: To ask a doctor for medication

- This option suggests a literal action related to medication, which doesn't relate to the idiomatic usage.

- Option 2: To drink cold water

- While drinking cold water might physically cool you, it isn't connected to the idiomatic meaning.

- Option 3: To gulp a tablet for a cold

- This option is misleading as it focuses on a literal action rather than the figurative meaning of calming down.

- Your interpretation of the idiom is spot on. Your answer is right!