Question:
\(K_2[HgI_4]\) detects the following ion:
\(K_2[HgI_4]\) detects the following ion:
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Nessler's reagent (\(K_2[HgI_4]\)) → test for NH\(_4^+\) (brown precipitate).
Updated On: Apr 16, 2026
- Cl\(^{-}\)
- NO\(_2^{-}\)
- NO\(_3^{-}\)
- NH\(_4^{+}\)
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The Correct Option is D
Solution and Explanation
Concept:
\(K_2[HgI_4]\) (potassium tetraiodomercurate(II)) is known as Nessler's reagent.
Step 1: Use of Nessler's reagent. It is used to detect the presence of ammonia (NH\(_3\)) or ammonium ions (NH\(_4^+\)).
Step 2: Reaction and observation. When Nessler's reagent is added to a solution containing NH\(_4^+\), a brown precipitate (or yellow coloration) is formed: \[ NH_4^+ + 2[HgI_4]^{2-} + 4OH^- \rightarrow NH_2Hg_2I_3 \downarrow (\text{brown}) + 7I^- + 3H_2O \]
Step 3: Why not other ions? Cl\(^-\), NO\(_2^-\), NO\(_3^-\) do not give a positive test with Nessler's reagent.
Step 1: Use of Nessler's reagent. It is used to detect the presence of ammonia (NH\(_3\)) or ammonium ions (NH\(_4^+\)).
Step 2: Reaction and observation. When Nessler's reagent is added to a solution containing NH\(_4^+\), a brown precipitate (or yellow coloration) is formed: \[ NH_4^+ + 2[HgI_4]^{2-} + 4OH^- \rightarrow NH_2Hg_2I_3 \downarrow (\text{brown}) + 7I^- + 3H_2O \]
Step 3: Why not other ions? Cl\(^-\), NO\(_2^-\), NO\(_3^-\) do not give a positive test with Nessler's reagent.
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