Final answer:
The compound that requires the least amount of acidified KMnO₄ for oxidation is FeSO₄, as only the iron(II) ion is oxidized and the sulfate ligand does not require additional oxidizing agent.
Step-by-step explanation:
Assuming complete ionization, the compound that will require the least amount of acidified KMnO₄ for complete oxidation can be determined by comparing the stoichiometry of the redox reactions each compound will undergo with KMnO₄. Acidified KMnO₄ acts as an oxidizing agent, converting Fe(II) to Fe(III). In a redox reaction, the number of moles of electron transferred is an important factor to consider.
The number of electrons each iron compound will transfer when it is oxidized by KMnO₄ is critical. For FeC₂O₄ (oxalate) and FeSO₃ (sulfite), two electrons per mole of Fe(II) are involved, as both C₂O₄²⁻ and SO₃²⁻ can be further oxidized. In contrast, Fe(NO₂)₂ (nitrite) and FeSO₄ (sulfate) involve only one electron transfer per mole of Fe(II), as NO₂⁻ and SO₄²⁻ are not oxidizable under these conditions.
Considering these reactions, FeSO₄ will require the least amount of KMnO₄ because only the Fe(II) ion is oxidized, without any associated ligand that would require additional KMnO₄ for oxidation. Thus, the correct answer is C. FeSO₄.