Why are pentahalides more covalent than trihalides?

Explanation

According to Fajan's rules, covalent character increases with decrease in size of covalent `E^(5+)` (E=element of group 15) is smaller than `E^(3+)`. Therefore pentahalides in which element is in `+5`oxidation state are more covalent than trihalides m which the element is in `+3` oxidation state.