As mentioned in the explanation of the previous question, if the standard electrode potential is higher than zero, then reduced form is more stable than the H₂ gas. The positive value of the standard electrode potential means that the ions of the element can oxidise hydrogen, or hydrogen ions can reduce the atoms. The higher the positive value, the more the ability of oxidation. The equation of formation of reduced form of MnO^4- is given by the equation MnO₄^- + 8H⁺ + 5e^-→ Mn²⁺ + 2e^-. The standard electrode potential is 1.51V which is highest and most positive. Option (iii) is the correct answer.