JEE Main levelSingle correct optionDifficulty 2 of 3ec27
The mercury button cell (Zn(Hg)∣ZnO,KOH∣HgO∣Hg) gives a nearly constant voltage during its life because
Amercury is a liquid and keeps the electrode area constant
Bthe overall reaction Zn(Hg)+HgOZnO+Hg involves only solids and liquids, so no ion concentration changes
CKOH is present in large excess
Dzinc amalgam has a very low overpotential
Answer: B
In the Nernst equation only species whose activity changes appear in Q. Here every reactant and product is a pure solid or liquid of unit activity, so E stays at E∘ until the reactants are exhausted.