The correct order of polarising ability of cations of Alkaline earth metals is

As the size of cation decreases nuclear charge increases, and hence distortion in the electron cloud of anion by the cation increases, hence polarising power increasesPolarising power of cationThe ability of a cation to cause distortion in the electron cloud of anion is called polarising power As the polarising power of cation increases sharing of electron between bonded atoms increases and hence covalent character increases