If Fe₄S₄ is used in brown ring tests for nitrates and nitrites. In this test, a freshly prepared Fe₄S₄ solution is mixed with a solution containing NO₂⁻ and NO₃⁻ and the conc. H₂SO₄ is run down the side of the test tube. If the mixture gets hot or is shaken,

• (I) the brown colour disappear
• (II) NO is evolved
• (III) a yellow solution of Fe₂(SO₄)₃ appears

A. I, II, III correct

B. I, III correct

C. II, III correct

D. only I correct

The brown ring test is a qualitative analysis method used to detect the presence of nitrates (NO₃⁻) and nitrites (NO₂⁻) in a solution. When Fe₄S₄ is added to the sample and concentrated sulfuric acid (H₂SO₄) is introduced, a series of reactions occur.

Reactions in the Brown Ring Test

Upon mixing, the following observations can be made:

• Disappearance of Brown Color: The initial brown color may fade when the mixture is heated or shaken, indicating a reaction is taking place.
• Evolving Nitric Oxide: Nitric oxide (NO) is produced during the reaction, which is a key indicator of the presence of nitrates or nitrites.
• Formation of Yellow Solution: The yellow solution of Fe₂(SO₄)₃ appears as a result of the reaction with sulfuric acid.

Correct Options Analysis

Based on the observations:

• Statement I is correct: The brown color disappears.
• Statement II is correct: NO is evolved.
• Statement III is correct: A yellow solution of Fe₂(SO₄)₃ appears.

Therefore, the correct answer is A. I, II, III correct.