(a) Due to smaller size and high poalrising power of Li+ ion ,LiCl is more covalent than KCl.
(b) Small cation Li+ ion highly polarizes large anion I-, LiI is more covalent and hence has lower melting point.
(c) Due to pseudo inert gas configuration, Cu+ is more polarizing than Na+ and hence CuCl is more Covalent NaCl.