i) Yes, L can compel only Y to pay ₹ 90,000/- since as per Section 43 of the Indian Contract Act, 1872, in the absence of express agreement to the contrary, the promisee may compel any one or more of the joint promisors to perform the whole of the promise.

ii) As per Section 42, when two or more persons have made a joint promise, then, unless a contrary intention appears by the contract, all such persons, during their joint lives and after the death of any of them, his representative jointly with the survivor or survivors and after the death of last survivor, the representatives of all jointly must fulfill the promise.

iii) According to Section 44, where two or more persons have made a joint promise, a release of one of such joint promisors by the promisee does not discharge the other joint promisor or joint promisors, neither does it free the joint promisors so released from responsibility to the other joint promisor or promisors. In this case, the release of X does not discharge Y and Z from their liability. Y and Z remain liable to pay the entire amount of ₹ 90,000 to L. And though X is not liable to pay to L, but he remains liable to pay to Y and Z i.e. he is liable to make the contribution to the other joint promisors.