Which one of the following reactions does NOT belong to "Lassaigne's test"?

Question

Accepted Answer

B. 1. **Recall the purpose of Lassaigne's test.**

Lassaigne's test is a qualitative technique used to detect the presence of **nitrogen, sulphur, halogens, and phosphorus** in an organic compound by fusing it with sodium metal to convert these elements into water-soluble sodium salts.

2. **Recall the typical reactions involved in this test.**

When an organic compound containing these elements is fused with sodium, characteristic reactions occur, such as:

$$
\mathrm{Na} + \mathrm{C} + \mathrm{N} \xrightarrow{\Delta} \mathrm{NaCN}
$$

$$
2\mathrm{Na} + \mathrm{S} \xrightarrow{\Delta} \mathrm{Na_2S}
$$

$$
\mathrm{Na} + \mathrm{X} \xrightarrow{\Delta} \mathrm{NaX}\ (\mathrm{X} = \mathrm{Cl, Br, I})
$$

These all involve **sodium reacting directly with the elements present in the organic compound** to form detectable sodium salts.

3. **Examine option B and see if it fits this pattern.**

The reaction $2\mathrm{CuO} + \mathrm{C} \xrightarrow{\Delta} 2\mathrm{Cu} + \mathrm{CO_2}$ involves **copper oxide reacting with carbon**, which is unrelated to sodium fusion and does not detect nitrogen, sulphur, phosphorus, or halogens. This reaction is not part of Lassaigne's test at all.

4. **Conclude which reaction does not belong.**

Hence, the reaction in option B does not belong to Lassaigne's test.