Select the most appropriate option to fill in the blank.

He is addicted to alcohol and exerts a bad influence ______ his family.

on

The correct option to fill in the blank is on.

The word "on" is used to indicate a direct effect or influence. In this case, the man's addiction to alcohol is directly affecting his family.

The other options are incorrect.

• For is used to indicate a purpose or reason. For example, "He drinks alcohol for pleasure."
• About is used to indicate a topic or subject matter. For example, "He talks about his addiction to alcohol all the time."
• In is used to indicate a location or position. For example, "He drinks alcohol in bars."