When aqueous $K C N$ is added to a solution of $C u S O_{4}$ , a white precipitate soluble in excess of $K C N$ is formed. No precipitate is formed when $H_{2} S$ gas is bubbled through the solution at this point because stable $[C u (C N)_{4}]^{3 -}$ does not ionize to give $C u^{+}$ .
If true enter 1, else enter 0.

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Solution

When aqueous KCN is added to a solution of $C u S O_{4}$ , a white precipitate soluble in excess of KCN is formed. The reactions are given below:
$C u S O_{4} + 2 K C N \to C u (C N)_{2} w h i t e p p t + K_{2} S O_{4}$
$C u (C N)_{2} + K C N \to K_{3} [C u (C N)_{4}] s t a b l e$
However, no precipitate is formed when $H_{2} S$ gas is bubbled through the solution at this point.
$K_{3} [C u (C N)_{4}] ⇌ 3 K^{+} [C u (C N)_{4}]^{3 -}$
Stable $[C u (C N)_{4}]^{3 -}$ does not ionize to give $C u^{+}$ , hence, no precipitate with $H_{2} S$ gas.
Therefore, the correct answer is 1.

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When aqueous KCN is added to a solution of CuSO4, a white precipitate soluble in excess of KCN is formed. No precipitate is formed when H2S gas is bubbled through the solution at this point because stable [Cu(CN)4]3− does not ionize to give Cu+.If true enter 1, else enter 0.