The electrode material composed of Hg(L) and Hg2Cl2(S) is inserted in a saturated KCl solution where the concentration of KCl solution is constant. If the concentration of a substance arising from nernst's equation does not change, its potential remains the same (assuming that the ambient temperature is constant).

Why is the concentration of KCl solution constant?

When the electrode reaction happens, the chloride concentration changes. And according to the nernst equation of potential is only related to the chloride ion concentration answer buy calomel electrode, with a saturated KCl solution, saturated KCl solution can match with KCl solid in saturated KCl solution, so it can keep the Cl - concentration is not disorderly is nernst equation potential only related to the chloride ion concentration, but it can't exist alone Cl -. K+ had to stay with it.