Explanation:

- Option 1: Void

- An agreement on behalf of a minor to act in an adult movie is against public policy and the law, making it void.

- A contract involving illegal activities or exploitation of minors holds no legal standing.

- This is the correct option.

- Option 2: Voidable

- A voidable contract means it can be canceled by one party.

- However, a contract that is void cannot be voidable.

- Option 3: Valid

- A valid agreement requires lawful consideration and intention, which is missing here.

- Option 4: Contingent

- A contingent contract depends on uncertain future events.

- This agreement does not fall under this category.