Precipitation tests identify Fe³⁺ and SO₄²⁻ in X Steps:

• Red-brown precipitate with NaOH indicates Fe³⁺ cation, as Fe(OH)₃ forms reddish-brown hydroxide.
• White precipitate with Ba(NO₃)₂ indicates SO₄²⁻ anion, as BaSO₄ is insoluble and white.
• White precipitate with dilute HNO₃ aligns with iron(III) sulfate behavior in acidic conditions, distinguishing from reducing ions like Cr²⁺ or Fe²⁺. Why D is correct:
• Iron(III) sulfate, Fe₂(SO₄)₃, yields red-brown Fe(OH)₃ with NaOH per solubility rules for metal hydroxides. Why the others are wrong:
• A: Chromium(II) sulfate yields blue Cr(OH)₂ with NaOH, not red-brown.
• B: Chromium(III) chloride yields gray-green Cr(OH)₃ with NaOH and no BaSO₄ with Ba(NO₃)₂, as Cl⁻ is soluble.
• C: Iron(II) sulfate yields green Fe(OH)₂ with NaOH, not red-brown. Final answer: D