Question

 PCl5 exists but Ncl5 does not why?​

Answer 1

Because hybridisation of NCl5 is sp3d but it has no d orbital in the second energy level so cannot form NCl5 whereas in PCl5 the hybridisation is the same i.e sp3d and it has got vacant d orbital so it can form PCl5

Answer 2

➡Nitrogen is a 2nd period element which has no vacant d-orbital whereas Phosphorus is the element of 3rd period which has vacant d-orbital. Hence Phosphorus can form bonds with 5 Chlorine atoms but Nitrogen can't.