Consider the following standard electrode potentials (`E^(@)` in volts) in aqueous solution:
`{:(underline("Element"), M^(3+)//M, M^(+)//M), ("Al", -1.66, + 0.55), (Tl, +1.26, -0.34):}`
Based on these data, which of the following statements is correct ?

Options

A. `Tl^(3+)` is more stable than `Al^(3+)`
B. `Al^(+)` is more stable then `Al^(3+)`
C. `Tl^(3+)` is more stable than `Al^(3+)`
D. `Tl^(+)` is more stable than `Al^(+)`

Answer

To solve the problem, we need to analyze the given standard electrode potentials for Aluminium (Al) and Thallium (Tl) and determine which statements regarding their stability are correct based on these values.

### Step-by-Step Solution:

1. **Identify the Given Electrode Potentials**:
- For Aluminium:
- \( \text{Al}^{3+} + 3e^- \rightarrow \text{Al} \) has \( E^\circ = -1.66 \, \text{V} \)
- \( \text{Al}^+ + e^- \rightarrow \text{Al} \) has \( E^\circ = +0.55 \, \text{V} \)

- For Thallium:
- \( \text{Tl}^{3+} + 3e^- \rightarrow \text{Tl} \) has \( E^\circ = +1.26 \, \text{V} \)
- \( \text{Tl}^+ + e^- \rightarrow \text{Tl} \) has \( E^\circ = -0.34 \, \text{V} \)

2. **Understanding Reduction Potentials**:
- Reduction potentials indicate the tendency of a species to gain electrons (be reduced). A higher (more positive) reduction potential means a greater tendency to be reduced.
- Conversely, a lower (more negative) reduction potential indicates a lesser tendency to gain electrons and thus a more stable oxidized form.

3. **Comparing Stability of \( \text{M}^+ \) and \( \text{M}^{3+} \)**:
- For \( \text{Al}^+ \) and \( \text{Tl}^+ \):
- \( E^\circ \) for \( \text{Al}^+ \) is \( +0.55 \, \text{V} \) (more positive, thus less stable than \( \text{Tl}^+ \))
- \( E^\circ \) for \( \text{Tl}^+ \) is \( -0.34 \, \text{V} \) (less positive, thus more stable than \( \text{Al}^+ \))
- Conclusion: \( \text{Tl}^+ \) is more stable than \( \text{Al}^+ \).

- For \( \text{Al}^{3+} \) and \( \text{Tl}^{3+} \):
- \( E^\circ \) for \( \text{Al}^{3+} \) is \( -1.66 \, \text{V} \) (more negative, thus more stable than \( \text{Tl}^{3+} \))
- \( E^\circ \) for \( \text{Tl}^{3+} \) is \( +1.26 \, \text{V} \) (more positive, thus less stable than \( \text{Al}^{3+} \))
- Conclusion: \( \text{Al}^{3+} \) is more stable than \( \text{Tl}^{3+} \).

4. **Final Conclusion**:
- Based on the analysis, we can conclude that:
- \( \text{Tl}^+ \) is more stable than \( \text{Al}^+ \).
- \( \text{Al}^{3+} \) is more stable than \( \text{Tl}^{3+} \).
- The correct statement based on the given options is that \( \text{Tl}^+ \) is more stable than \( \text{Al}^+ \).