Which of the 2 dissolution processes is more exothermic, on a kJ/mol basis?

We can consider the enthalpy of solution to be the sum of two terms: the expansion of the ionic lattice and the solvation energy of the ions. Since the two compounds have the same lattice energy, the expansion term is equal. Then, dissolving A in water releases more energy, because energy is given off when the ions are solvated by water.