The correct option is : (c) less than -57.33 kJ mol-1
Explanation:
MgO is the oxide of weak base and we know that heat of neutralisation of 1 eq. of strong acid with strong base is - 57.33 kJ/mol.
=> with weak base some heat is absorbed in dissociation of weak base.
=> Heat of neutralisation of weak base with strong acid will be less than - 57.33 kJ/mol.