Zinc ion confirmatory tests with reagents

Steps:

• Identify Zn²⁺ ions in ZnCl₂(aq) solution.
• Add aqueous ammonia: initial white Zn(OH)₂ precipitate forms, dissolves in excess to [Zn(NH₃)₄]²⁺ complex.
• Evaluate other reagents against Zn²⁺ behavior.
• Select matching observation.

Why B is correct:

• Zn²⁺ forms amphoteric hydroxide soluble in excess NH₃ due to stable tetraamminezinc(II) complex [Zn(NH₃)₄]²⁺.

Why the others are wrong:

• A: No SO₄²⁻ in ZnCl₂, so acidified Ba(NO₃)₂ yields no BaSO₄ precipitate.
• C: Zn(OH)₂ dissolves in excess NaOH forming [Zn(OH)₄]²⁻, so it is soluble.
• D: Cu displaces nothing from ZnCl₂ as Zn is more reactive; no precipitate forms.

Final answer: B