\(PCl_5\) is well known but \(NCl_5\) is not because nitrogen does not have vacant d-orbitals in its valence shell.
So, nitrogen cannot expand its octet.
On the other hand phosphorus has vacant d-orbitals in its valence shell which enables it to expand its octet.
Therefore, the correct option is (B): nitrogen doesn’t have d-orbitals in its valence shell.
Consider the following sequence of reactions : 
Molar mass of the product formed (A) is ______ g mol\(^{-1}\).