how many valence electrons in V?

The electronic configuration of vanadium (V) is :
1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s²

The valence electrons include two outermost 4s electrons and three low-lying 3d electrons. Therefore, vanadium has FIVE valence electrons.

All the five valence electrons when the oxidation number of vanadium is +5. For example, in VO₂⁺ ([O=V=O]⁺), one valence electron is lost to make a singly positive ion, and the rest four valence electrons are used to make two V=O double bonds.