Question 11A.CQ.5: Why does not nitrogen form pentahalides like phosphorus ?...

Nitrogen does not have vacant d-orbitals in its valence shell. Therefore, it cannot extend its valency beyond 3. Therefore, it can form maximum of four bonds and cannot form pentahalides. On the other hand, phosphorus has vacant 3d-orbitals in the valence shell and therefore, one electron can be easily promoted from valence 3s-orbital to vacant 3d-orbital. Thus, it can exhibit pentavalency in its compounds.