Question: 90. Which one of the following reactions does NOT belong to “Lassaigne’s test”?
(1) \mathrm{Na}+\mathrm{C}+\mathrm{N} \xrightarrow[\Delta]{ } \mathrm{NaCN}
(2) 2 \mathrm{Na}+\mathrm{S} \xrightarrow[\Delta]{ } \mathrm{Na}_{2} \mathrm{~S}
(3) \mathrm{Na}+\mathrm{X} \xrightarrow[\Delta]{ } \mathrm{NaX}
(4) 2 \mathrm{CuO}+\mathrm{C} \xrightarrow[\Delta]{ } 2 \mathrm{Cu}+\mathrm{CO}_{2}
Answer: Option (4)
Explanation:
Lassaigne’s test is used for the detection of extra elements like nitrogen,
sulphur and halogens in an organic compound.
In this test, the organic compound is fused with sodium metal so that these elements are converted into water-soluble sodium salts.
Reaction (1) represents the formation of sodium cyanide during sodium fusion when carbon and nitrogen are present in the organic compound.
Reaction (2) represents the formation of sodium sulphide when sulphur is present in the organic compound.
Reaction (3) represents the formation of sodium halide when a halogen \mathrm{X} is present in the organic compound.
All these reactions are essential steps of Lassaigne’s test.
Reaction (4) represents the reduction of copper(II) oxide by carbon to form copper and carbon dioxide.
This reaction is not related to sodium fusion or detection of extra elements in Lassaigne’s test.
Therefore, reaction (4) does not belong to Lassaigne’s test.