Explanation:

- Option 1: If any party wishes so

An arbitration agreement usually requires mutual consent. It is not valid if only one party wishes to refer disputes to arbitration. Therefore, this option is insufficient.

- Option 2: If it is in writing

A written arbitration agreement is generally necessary for it to be legally enforceable. This ensures clarity and serves as evidence of consent from both parties.

- Option 3: Either (a) or (b)

This option suggests that either of the above conditions would suffice. However, only written agreements are usually acceptable, not merely individual wishes.

- Option 4: Neither (a) nor (b)

This is incorrect as it dismisses the necessity of a written agreement, which is often required.