The reaction at cathode in the cells commonly used in clocks involves.
oxidation of Mn from \( +2 \) to \( +7 \)
reduction of Mn from \( +4 \) to \( +3 \)
reduction of Mn from \( +7 \) to \( +2 \)
oxidation of Mn from \( +3 \) to \( +4 \)