Question

Consider the following standard electrode potentials (\(E^\circ\) in volts) in aqueous solution: \includegraphics[]{135.png} Based on this data, which of the following statements is correct?

• A. \( Tl^{3+} \) is more stable than \( Al^{3+} \)
• B. \( Tl^{1+} \) is more stable than \( Al^{3+} \)
• C. \( Al^{1+} \) is more stable than \( Al^{3+} \)
• D. \( Tl^{1+} \) is more stable than \( Al^{1+} \)

Hint:

Lower oxidation states of thallium (Tl) are more stable due to the inert pair effect, while higher oxidation states of aluminum (Al) are more stable due to stronger metallic bonding.

Answer 1

The Correct Option is D

Step 1: Understanding Electrode Potentials 
- Negative \(E^\circ\) means the ion is stable in its oxidized form. 
- Positive \(E^\circ\) means the ion is easily reduced, implying instability in oxidized form.
Step 2: Stability of \( Al^{3+} \) vs. \( Al^+ \) 
- \(E^\circ\) for \( Al^{3+}/Al \) is -1.66 V, so \( Al^{3+} \) is stable. 
- \(E^\circ\) for \( Al^+/Al \) is +0.55 V, so \( Al^+ \) is unstable. 
\( Al^{3+} \) is more stable than \( Al^+ \) → Eliminates Option (3).
Step 3: Stability of \( Tl^{3+} \) vs. \( Tl^+ \) 
- \(E^\circ\) for \( Tl^{3+}/Tl \) is +1.26 V, so \( Tl^{3+} \) is unstable. 
- \(E^\circ\) for \( Tl^+/Tl \) is -0.34 V, so \( Tl^+ \) is stable. 
\( Tl^+ \) is more stable than \( Tl^{3+} \) → Eliminates Option (1).
Step 4: Comparing \( Tl^+ \) and \( Al^+ \) 
- \( Al^+ \) is highly unstable. 
- \( Tl^+ \) is relatively stable. 
\( Tl^+ \) is more stable than \( Al^+ \) → Confirms Option (4) as the correct answer.