For each of the following reactions, balance reaction, determine the number of electrons transferred in the reaction, and write the equilibrium constant expression:
a. Na (s) + H2O (l) ! NaOH (aq) + H2 (g)
b. AgCl (s) + H2 (g) ! HCl (aq) + Ag (s)
c. MnO2 (s) + O2 (g) + H2O (l) ! H+ (aq) + MnO4- (aq).