Question

LiCl is more covalent than KCl. Why ?

Answer 1

This is the best answer
Since in this case cl is common so deciding factor will be Li or K so according to Fajans rule smaller the cation and larger the anion more covalent character will be there and since Li is smaller than K so it will have more covalent character

If you really want to know the reason,refer below
If we observe the periodic table we will see that group wise Li is above K which means the size of lithium is smaller than K and we know that the smaller cations can distort the electron cloud of the anions more than the big sized cations. So lithium can distort the electron more and attract cl to it more to form a strong covalent bond