Why V can't have the valence 7 by taking an electron from the 3p orbital and putting it into 3d?
Vanadium has a stable valency of 5.
Electrons cannot be transferred from $3p$ orbital to $3d$ orbital as the $3p$ orbital is completely filled and has attained stability.
It requires high energy so as to transfer electrons from $3p$ orbital to $3d$ orbital.
Hence,Vanadium has a valency of 5 only and not of 7 or 6.