The calomel and quinhydrone electrodes are reversible with respect to which ions, respectively ?

Options

A. `Cl^(c-),H^(o+)`
B. `H^(o+),Cl^(c-)`
C. `Hg_(2)^(2+),overset(c-)(O)H`
D. `Hg_(2)^(2+),H^(o+)`

Explanation

To determine the ions with which the calomel and quinhydrone electrodes are reversible, we can analyze each electrode's behavior and the reactions involved.

### Step-by-Step Solution:

1. **Understanding the Calomel Electrode:**
- The calomel electrode consists of mercury(I) chloride (Hg2Cl2) in contact with mercury (Hg) and a chloride ion solution (Cl-).
- The half-reaction for the calomel electrode when it acts as a cathode is:
\[ \text{Hg}_2\text{Cl}_2 + 2e^- \rightarrow 2\text{Hg} + 2\text{Cl}^- \]
- This reaction shows that the potential of the calomel electrode is dependent on the concentration of chloride ions (Cl-).

2. **Nernst Equation for Calomel Electrode:**
- The Nernst equation for the calomel electrode can be expressed as:
\[ E_{\text{cell}} = E^\circ_{\text{cell}} - \frac{0.059}{n} \log [\text{Cl}^-] \]
- Here, \(n\) is the number of electrons transferred (which is 2 in this case). The equation indicates that the cell potential is influenced by the concentration of Cl- ions.

3. **Conclusion for Calomel Electrode:**
- Therefore, the calomel electrode is reversible with respect to **Cl- ions**.

4. **Understanding the Quinhydrone Electrode:**
- The quinhydrone electrode is based on a compound that can undergo oxidation and reduction involving protons (H+).
- When the quinhydrone electrode acts as an anode, the half-reaction is:
\[ \text{C}_6\text{H}_6\text{O}_2 \rightarrow \text{C}_6\text{H}_4\text{O}_2 + 2\text{H}^+ + 2e^- \]
- This reaction shows that the potential of the quinhydrone electrode is dependent on the concentration of hydrogen ions (H+).

5. **Nernst Equation for Quinhydrone Electrode:**
- The Nernst equation for the quinhydrone electrode can be expressed as:
\[ E_{\text{cell}} = E^\circ_{\text{cell}} - \frac{0.059}{n} \log [\text{H}^+] \]
- Again, \(n\) is the number of electrons transferred (which is 2). The equation indicates that the cell potential is influenced by the concentration of H+ ions.

6. **Conclusion for Quinhydrone Electrode:**
- Therefore, the quinhydrone electrode is reversible with respect to **H+ ions**.

### Final Answer:
The calomel electrode is reversible with respect to **Cl- ions**, and the quinhydrone electrode is reversible with respect to **H+ ions**.