The correct answer is C. He is bound to restore it or make compensation for it to the person from whom he received it.
An agreement is void if it is not made with the free consent of the parties or if it is for an unlawful object or if it is impossible to perform. If an agreement is void, then the parties are not bound by it and cannot enforce it. However, if one party has received an advantage under the agreement, then they are bound to restore it or make compensation for it to the other party. This is because the law does not want to allow one party to benefit from an agreement that is not binding on them.
Option A is incorrect because the person who has received the advantage does not need the prior approval of the other party to retain it. The other party cannot enforce the agreement, so they cannot demand that the advantage be returned.
Option B is incorrect because the person who has received the advantage is not allowed to retain it without any prior permission. The law requires them to restore it or make compensation for it.
Option D is incorrect because the person who has received the advantage is not only bound to restore it or make compensation for it when a court order is passed in this behalf. They are bound to do so even if there is no court order.