Compound identification via solubility and specific tests for barium and nitrate ions

Steps:

• Solubility in water indicates a soluble salt like nitrates or chlorides of ammonium or barium.
• White precipitate with dilute H2SO4 confirms Ba²⁺ ion, forming insoluble BaSO₄.
• Gas turning damp red litmus blue is ammonia (NH₃), produced by reduction of NO₃⁻ with Al in NaOH.
• Thus, Q contains both Ba²⁺ and NO₃⁻, matching Ba(NO₃)₂.

Why D is correct:

• Ba(NO₃)₂ is water-soluble, forms white BaSO₄ precipitate with H₂SO₄, and its nitrate reduces to NH₃ with Al/NaOH.

Why the others are wrong:

• A: NH₄Cl forms no precipitate with H₂SO₄ (soluble NH₄₂SO₄) and lacks NO₃⁻ for the specific Al reduction test.
• B: Duplicate of D, but if distinct, lacks unique mismatch; assumes error in listing.
• C: NH₄NO₃ produces NH₃ but forms no white precipitate with H₂SO₄ (soluble (NH₄)₂SO₄).

Final answer: D