Consider the following standard electrode potentials (E⁰ in volts) in aqueous solution:
Element M³⁺/M M⁺/M
Al -1.66 +0.55
Tl +1.26 -0.34
Based on these data, which of the following statements is correct?

The standard reduction potentials are given as:
Al³⁺ + 3e⁻ → Al E⁰ = -1.66 V
Al⁺ + e⁻ → Al E⁰ = +0.55 V
Tl³⁺ + 3e⁻ → Tl E⁰ = +1.26 V
Tl⁺ + e⁻ → Tl E⁰ = -0.34 V

A more positive reduction potential indicates a greater tendency for reduction (gain of electrons) and thus greater stability of the oxidized species. Let's analyze the stability:

Comparing Al³⁺ and Al⁺: The reduction potential for Al³⁺ + 3e⁻ → Al is -1.66V, while for Al⁺ + e⁻ → Al is +0.55V. The more positive value for Al⁺ indicates that Al⁺ is more stable than Al³⁺.

Comparing Tl³⁺ and Tl⁺: The reduction potential for Tl³⁺ + 3e⁻ → Tl is +1.26V, while for Tl⁺ + e⁻ → Tl is -0.34V. The more positive value for Tl³⁺ indicates that Tl³⁺ is more stable than Tl⁺.

Comparing Al⁺ and Tl⁺: The reduction potential for Al⁺ + e⁻ → Al is +0.55V, while for Tl⁺ + e⁻ → Tl is -0.34V. The more positive value for Al⁺ again indicates that Al⁺ is more stable than Tl⁺.

Therefore, based on these data, the correct statement is that Al⁺ is more stable than Al³⁺, and Tl⁺ is more stable than Al⁺.