Though nitrogen exhibits + 5 oxidation state, it does not form penta-halide. Given reason.

Explanation

Due to the presence of five valence electrons nitrogen shows an oxidation state of +5. in `N_2 O_5`. Nitrogen with n=2 (i.e., second shell) has s and p-orbitals only as shown below. N(Z = 7): `1s^2 2s^2 2p^3`
It does not have d-orbitals to expand its covalency beyond four. That is why it does not form pentahalides like other members of its group (e.g., `PCl_5` etc.)