While Fe^3+ is stable, Mn^3+ is not stable in acid solution because — Electrochemistry Chemistry Question

💡 Solution & Explanation

A metal ion is unstable in aqueous solution if it can spontaneously oxidize water to oxygen gas. The standard reduction potential of Mn^3+/Mn^2+ (1.50 V) is greater than the standard reduction potential of O2/H2O (1.23 V), meaning Mn^3+ is a sufficiently strong oxidizing agent to oxidize water to O2. Conversely, Fe^3+/Fe^2+ (0.77 V) is lower than 1.23 V, so it cannot oxidize water and remains stable. Therefore, correct answer is D.