Which one of the following reactions does NOT belong to “Lassaigne’s test”?

Question

Question

This question was previously asked in

NEET 2025 Official Paper (Held On: 04 May, 2025)

Answer 1

CONCEPT:

Lassaigne’s Test

Lassaigne’s test is a qualitative test used to detect the presence of elements such as nitrogen (N), sulfur (S), and halogens (X) in an organic compound.
In this test, the organic compound is fused with sodium metal, converting these elements into their respective sodium salts (e.g., NaCN, Na₂S, NaX), which can be detected by characteristic reactions.
The test involves heating the mixture to allow the reaction of sodium with the element present in the organic compound.
Nitrogen, sulphur, and halogens present in organic compounds are detected by Lassaigne’s test. Here, a small piece of Na metal is heated in a fusion tube with the organic compound. The principle is that, in doing so, Na converts all the elements present into ionic form.

Na + C + N → NaCN
2Na + S → Na2S
Na + X → NaX ( X= Cl, Br, or I)
The formed ionic salts are extracted from the fused mass by boiling it with distilled water. This is called sodium fusion extract.

EXPLANATION:

Na + C + N → NaCN: This reaction forms sodium cyanide, used to detect nitrogen in the compound. This belongs to Lassaigne’s test.
2Na + S → Na₂S: This forms sodium sulfide, used to detect sulfur. This also belongs to Lassaigne’s test.
Na + X → NaX: This forms sodium halide, used to detect halogens like Cl, Br, and I. This belongs to Lassaigne’s test.
2CuO + C → 2Cu + CO₂: This reaction involves the reduction of copper oxide by carbon and is unrelated to Lassaigne’s test for detecting N, S, or halogens.

Therefore, the reaction that does NOT belong to Lassaigne’s test is 2CuO + C → 2Cu + CO₂