Question

Treatment of a gas \(X\) with a freshly prepared ferrous sulphate solution gives a compound \(Y\) as a brown ring. The compounds \(X\) and \(Y\) are :

• A. \(NO\) and \([Fe(NO)]SO_4\)
• B. \(NO_2\) and \([Fe(NO_2)]SO_4\)
• C. \(N_2O\) and \([Fe(N_2O)]SO_4\)
• D. \(N_2O_4\) and \([Fe(N_2O_4)]SO_4\)

Answer 1

The Correct Option is A

Concept: The brown ring test is used for detection of nitrate ions. During the test:

• Nitrate ions are reduced to nitric oxide \(NO\).
• \(NO\) forms a complex with ferrous sulphate.

Step 1: {Formation of nitric oxide} \[ NO_3^- \rightarrow NO \] Step 2: {Complex formation} \[ Fe^{2+} + NO \rightarrow [Fe(NO)]^{2+} \] This complex appears as a brown ring at the interface. Thus \[ X = NO \] \[ Y = [Fe(NO)]SO_4 \]