Question

Pcl5 is known but Ncl5 is not known

Answer 1

Because Nitrogen has no vacant shell to accept electrons to form that compound

Answer 2

Phosphorous has d-orbitals & hence

can accommodate the electrons

from Cl into them,in case of N the

d-orbitals are absent & electrons can be

accommodated only in p-orbitals.Hence

PC15 exists.