Explanation:

- Reprimand: To formally criticize or rebuke someone. It's a negative action meant to express disapproval.

- Option 1, Apprehend: To arrest or understand something. It's unrelated to expressing approval or disapproval, so not an antonym.

- Option 2, Reproach: To express disapproval or disappointment. This is similar to reprimand, not the opposite.

- Option 3, Compliment: To praise or express approval. It's the direct opposite of reprimanding someone.

- Option 4, Blame: To hold someone responsible for a fault. This also shares a negative connotation similar to reprimand, not its opposite.