Chemistry - Complete P-block Question with Solution | TestHub

The oxidizing strength of an ion depends on its tendency to gain electrons. For Group 15 elements, the stability of the +5 oxidation state decreases down the group due to the inert pair effect. This means that Bi⁵⁺ is less stable than Sb⁵⁺ and thus has a stronger tendency to gain electrons and revert to the more stable +3 oxidation state, making it a stronger oxidizing agent.

The final answer is $\boxed{B{i}^{5+}}$.