69. Solving a chemistry problem

3. For a redox element of the type Pt│A, B││C, D│Pt at T = 298 K, according to the data given in the appendix on the standard electrode potentials of half-cells, write an equation and calculate the equilibrium constant of the oxidation-reduction reaction and the electromotive force element, if the activities of the substances in the solution are equal: aA, aB, aC and aD. (Table 35)

Option A B C D aA, aB, aC and aD

3 (MnO4)- (MnO4)2- (MnO4)- Mn2 0.009 0.014 0.001 0.07