NF3 is possible, but NF5 is not. Why?
According to the electronic configuration of nitrogen, it does not have 3d orbital that's why it can't expand the valency up to 5 and does not form .
N does not have vacant d orbitals. Hence, there is no excitation of ns2 electron to vacant orbitals. Thus, has only three unpaired electrons in p-orbitals showing +3 oxidation state and not +5 in halides like other elements of group.