Question

PCl5 is known but PI5 is not known. why?

Answer 1

Due to small size of Cl atom, five Cl atoms can be accommodated around P atom. But I is of large size and therefore, five I atoms cannot be accommodated around P atom. As a result, P - I bonds are weak and prefer to form PI3 rather than PI5.

Hope this helps:)

Answer 2

ya the reason is this that P is so small in size than I therefore PI5 not known.
While the Cl is also big in size than P but its less big in size than I therefore PCl5 is known.
I hope this is helpful for u;)