AIIMS 2018 Chemistry Redox Reactions MCQ Question

Fe⁵⁺ is the least stable species in aqueous medium due to its high charge density, which leads to significant instability and a strong tendency to hydrolyze or react with water, forming hydroxides or oxides. In contrast, Fe²⁺ and Fe³⁺ are more stable in aqueous solutions, with Fe²⁺ being easily oxidized to Fe³⁺, while Fe⁴⁺ is rarely encountered and is also less stable than Fe³⁺ due to its higher oxidation state. Thus, the increasing oxidation states beyond Fe³⁺, such as Fe⁴⁺ and Fe⁵⁺, become increasingly unstable in aqueous environments.