[lamhkbenny]

I have checked the reduction potential involving sulphite, it is -0.93V

SO₄^2-+2H⁺+2e--> SO₃^2- + H₂O

and
V(V) -> V(IV)   E= +1.00V
V(IV) -> V(III)   E= +0.34V
V(III) -> V(II)   E= -0.26V

But in practical, why sodium sulphite can only reduce the V(V) to V(III) only? But not V(II)?

Thanks !!