X is a metal sulfite forming a white hydroxide precipitate Steps:

• White precipitate with dilute NaOH indicates a cation like Al³⁺, Zn²⁺, or Ca²⁺ that forms an insoluble hydroxide.
• Gas evolving on warming with dilute HNO₃ that decolourises acidified KMnO₄ is SO₂, confirming SO₃²⁻ anion from a sulfite salt.
• No visible reaction (no precipitate) when adding dilute HNO₃ and Ba(NO₃)₂ shows absence of SO₄²⁻, as BaSO₄ would form in acid; SO₃²⁻ decomposes to SO₂ instead.
• Combining tests, X is Al₂(SO₃)₃, ZnSO₃, or CaSO₃.

Why D is correct:

• D lists the cations (Al³⁺, Zn²⁺) and Ca component fitting the hydroxide and sulfite tests, per qualitative analysis for insoluble metal hydroxides and SO₃²⁻ behavior.

Why the others are wrong:

• A: Al₂(SO₄)₃ contains SO₄²⁻, forming BaSO₄ precipitate in acid.
• B: CaSO₄ contains SO₄²⁻, forming BaSO₄; no SO₂ gas produced.
• C: Both Al₂(SO₄)₃ and ZnSO₄ contain SO₄²⁻, forming BaSO₄ precipitate.

Final answer: D