Q.
The standard electrode potential (M3+/M2+) for V,Cr,Mn & Co are −0.26V, −0.41V,+1.57V and +1.97V, respectively. The metal ions which can liberate H2 from a dilute acid are
Metal cation with (−) value of reduction potential (M+3/M+2) or with (+) value of oxidation potential (M+2/M+3) will liberate H2
Therefore they will reduce H+
i.eV +2 and Cr+2