The answer is (b). As, vanadium is attached to five fluoride atoms, each flouride containing -1 oxidation state, hence five fluoride contains -5, to neutralize, vanadium should have +5 oxidation state.
C. pain reliever
ex. tylenol, aleve, etc.
You need to monitor the solution to see when the crystals start gathering at the bottom of the solution. You can slowly add alum until it stops dissolving. The point just before it starts its sedimentation at the bottom is the point when the solution is saturated.