The correct option is A valid
Every promisee may dispense with or remit, wholly or in part, the performance of the promise made to him, or may extend the time for such performance, or may accept instead of it any satisfaction which he thinks fit as per section 63 of the Act. In this case, though the creditor i.e. Y has accepted to take the amount less than the originally owed amount, the agreement is valid as per section 63 of the Act.