Qualitative Analysis

Step 1: Understanding the Concept:
Brown ring test is a confirmatory test for nitrate ions.

Step 2: Detailed Explanation:
The test involves: NO + 3Fe + 4H → NO + 3Fe + 2H O;
Fe + NO → [Fe(H O) NO] (brown ring complex).

Step 3: Final Answer:

Step 1: Understanding the Concept:
Lassaigne's test is used for the detection of nitrogen, sulphur, and halogens in organic compounds. A blood red coloration indicates the presence of both nitrogen and sulphur.

Step 2: Detailed Explanation:
When an organic compound containing both N and S is fused with sodium, NaCNS (sodium thiocyanate) is formed. In Lassaigne's test, the extract is treated with FeCl . The Fe ions react with CNS to form Fe(CNS) , which is blood red in color. Among the given options, thiourea (H N-CS-NH ) contains both N and S, so it gives a positive test.

Step 3: Final Answer:
Thiourea gives a blood red coloration in the Lassaigne test, which corresponds to option (D).