Which of the following would be unenforceable because the subject matter is illegal?

Which of the following would be unenforceable because the subject matter is illegal? A contingent fee charged by an attorney to represent a plaintiff in a negligence action. An arbitration clause in a supply contract. A restrictive covenant in an employment contract prohibiting a former employee from using the employer’s trade secrets. An employer’s promise not to press embezzlement charges against an employee who agrees to make restitution.