What is the valency of vanadium?

Vanadium is a group 5 transition metal with d orbitals, but there's a simple answer and a better answer.

The simple answer is "+2, because it has the same +2 p orbital as the type 2 metals."

The better answer is "It depends, because d orbitals are strange. -1, +1, +2, +3, +4, and +5 are all possible oxidation states."

This is a general property of all transition metals; because the d orbitals have very close energy levels, they can allow different numbers of electrons to participate in a bond under different circumstances, and therefore different valences for the atom depending on what sort of bond it is in. This is part of what gives transition metals their unusual properties, such as their high electrical conductivity and their ability to alloy with one another.