Question:

Formation of $\mathrm{Na}_4\left[\mathrm{Fe}(\mathrm{CN})_5 \mathrm{NOS}\right]$, a purple coloured complex formed by addition of sodium nitroprusside in sodium carbonate extract of salt indicates the presence of :

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Sulphide ions give a purple colour with sodium nitroprusside.
Updated On: Oct 26, 2026
  • Sulphide ion
  • Sulphite ion
  • Sulphate ion
  • Sodium ion
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The Correct Option is A

Solution and Explanation

Sodium nitroprusside, $Na_2[Fe(CN)_5NO]$, reacts with sulphide ions in the sodium carbonate extract to give a purple colour:
$S^{2-} + [Fe(CN)_5NO]^{2-} \rightarrow [Fe(CN)_5NOS]^{4-}$ (that is, $Na_4[Fe(CN)_5NOS]$).
This is the test for sulphide ion: option (1).
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