The correct option is C illegal
Illegal agreements are those agreements, object or consideration of which is not enforceable by law and is punishable by the law. Hence, illegal agreements are void ab initio. On the other hand, the void agreements are not enforceable by the law and there is no legal recourse. However, performance of the agreement can be done as it is not strictly forbidden. Hence, this means that all illegal agreements are void in nature but it is not necessary that all void agreements are illegal.