# Why is it that in the case of nitrogen $\text{NCl}_3$ is possible, but not $\text{NCl}_5$, while in the case of phosphorus, $\text{PCl}_3$ and $\text{PCl}_5$ are possible.

$\begin{array}{1 1} \text{Due to the lower electronegativity of P than N} \\ \text{Due to the lower tendency of H-bond formation in P than N} \\ \text{Availability of vacant d orbitals in P but not in N} \\ \text{P occurs in solid state, while N is in gaseous state at room temperature}\end{array}$

Answer: Availability of vacant d orbitals in P but not in N
In phosphorus, the 3d-orbitals are available which means that it can form pentahalides also, but nitrogen cannot due to the absence of d-orbitals.
$_7\text{N} = 1s^2 2s^2 2p^3; \quad _{15}\text{P} = 1s^2 2s^2 2p^6 3s^2 3p^3$