Under The Hindu Adoptions and Maintenance Act, 1956, who among the following cannot be adopted?

Section 10(ii) of the Hindu Adoptions and Maintenance Act, 1956 provides that no person can be adopted unless he or she "has not already been adopted". So an "Already adopted child" cannot be adopted again.

Being a Hindu and being unmarried are conditions for adoption under section 10, and a minor can be adopted (ordinarily before the age of fifteen under section 10(iv)), so none of the following bars adoption.