Zinc ion test with ammonia

Steps:

• Identify Zn²⁺ as the cation in zinc chloride solution.
• Recall standard qualitative tests for Zn²⁺ ions.
• Apply ammonia test: forms Zn(OH)₂ white precipitate, dissolves in excess NH₃.
• Match to options, confirming B's description.

Why B is correct:

• Zn²⁺ + 2NH₃ + 2H₂O → Zn(OH)₂ (white ppt), then excess NH₃ forms soluble [Zn(NH₃)₄]²⁺ complex.

Why the others are wrong:

• A: Barium nitrate precipitates sulfates as BaSO₄; no sulfate in ZnCl₂, so no reaction.
• C: Zn(OH)₂ dissolves in excess NaOH to form [Zn(OH)₄]²⁻ zincate ion.
• D: Cu metal does not react with Zn²⁺; Zn is more reactive, no displacement or precipitate.

Final answer: B