Which of the following is not a valid arbitration agreement?

As per s.7 of the Arbitration & Conciliation act, 1996- S.7. Arbitration agreement.—(1) In this Part, “arbitration agreement” means an agreement by the  parties to submit to arbitration all or certain disputes which have arisen or which may arise between them in respect of a defined legal relationship, whether contractual or not. (2) An arbitration agreement may be in the form of an arbitration clause in a contract or in the form of a separate agreement. (3) An arbitration agreement shall be in writing. (4) An arbitration agreement is in writing if it is contained in— (a) a document signed by the parties; (b) an exchange of letters, telex, telegrams or other means of telecommunication [including communication through electronic means] which provide a record of the agreement; or (c) an exchange of statements of claim and defence in which the existence of the agreement is alleged by one party and not denied by the other. (5) The reference in a contract to a document containing an arbitration clause constitutes an  arbitration agreement if the contract is in writing and the reference is such as to make that arbitration clause part of the contract.