a
\(NF_5\) does not exist because \(N\) does not form pentahalides due to the absence of \(d-\) orbital in its valence shell. While \(P,\, As\) and \(Sb\) form pentahalides of the general formula \(MX_5\) (where, \(M = P,\, As\) and \(Sb\) ) due to the presence of vacant \(d-\) orbitals in their respective valence shell.