The standard electrode potential \( (\mathrm{M^{3+}} / \mathrm{M^{2+}}) \) for \( \mathrm{V} \), \( \mathrm{Cr} \), \( \mathrm{Mn} \) and \( \mathrm{Co} \) are \( -0.26 \ \mathrm{V} \), \( -0.41 \ \mathrm{V} \), \( +1.57 \ \mathrm{V} \) and \( +1.97 \ \mathrm{V} \), respectively. The metal ions which can liberate \( \mathrm{H_2} \) from a dilute acid are;
