Why is CuCl more covalent than NaCl?

Explanation

If the charge and size of the cations remain constant, the cation with pseudonoble gas (18 electron) configuration, as in case of `Cu^(2+)(3s^(2)3p^(6)3d^(10))` causes larger polarisation on the electron cloud of the anion than a cation with noble gas (8 electron) configuration, as in case of `Na^(+)(2s^(2)2p^(6))` becasue, (n-1)p electorns are more effective in shielding the outer electrons compared to the (n-1)d electrons. as a result, an appreciable increase in electron charge cloud density between the two nuclei takes place, leading to an increase in covalent character of the bond, ehnce, CuCl is more covalent than `NaCl`.