Question

Calomel electrode is reversible with respect to:
A. ${{H}^{+}}$ions
B. $Hg_{2}^{2+}$ions
C. $C{{l}^{-}}$ions
D. None of these

Answer 1

The capability of the calomel electrode relies on the concentration of the chloride ions in solution. On the off chance that the electrode is soaked calomel cathode (SCE), a crystals of $KCl$ are set over the $Hg-H{{g}_{2}}Cl_2$ paste so as to keep the solution saturated.

Complete answer:
Calomel electrode is a metal-sparingly dissolvable salt electrode. It is utilized as a secondary reference electrode to decide the standard potentials of the electrode. The electrode consists of a glass tube given a twisted side tube and another side tube B. A little Hg is put at the lower part of the dry glass tube. A rubber bung conveying a slender glass tube with a platinum wire is then embedded, taking into consideration that the platinum wire drips into mercury. The mercury is then covered with a layer of mercury and mercurous chloride (calomel) paste. The glass tube is then loaded up with a $KCl$ solution of definite concentration.
Calomel Electrode:
$Hg(l)/H{{g}_{2}}C{{l}_{2}}(s)/C{{l}^{-}}(aq)$
It is compared by a wire in contact with a paste of $Hg$ and $H{{g}_{2}}C{{l}_{2}}$ present in a $KCl$ solution,
Reaction: $Hg(l)/H{{g}_{2}}C{{l}_{2}}(s)/C{{l}^{-}}(aq)$
$\dfrac{1}{2}H{{g}_{2}}C{{l}_{2}}(s)+{{e}^{-}}\to Hg(l)+C{{l}^{-}}$
E=E^{\circ}-0.0591\log \left[ C{{l}^{\\_}} \right]

**Hence, the correct option is C. $Cl^-$ ions.

Note:**
The capability of calomel terminal reductions with increment in the concentration of chloride ions at a given temperature. In this manner, the terminal is reversible as for concentration of chloride ions. The calomel electrode is an example of a reversible system. Reversible electrodes are generally utilized as reference electrodes since the potential at the electrode is all around characterized, stable, and controllable.