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

The correct option is: 2CuO + C → 2Cu + CO₂

Explanation:
Lassaigne's test (also known as the sodium fusion test) is a general test used in qualitative organic analysis for the detection of extra elements like nitrogen (N), sulfur (S), and halogens (X = Cl, Br, I) in an organic compound.

During this test, the organic compound is heated strongly with a small piece of metallic sodium (Na). The sodium fuses with the elements present in the organic compound to form water-soluble ionic sodium salts:
1. Nitrogen reacts with sodium and carbon to form sodium cyanide:
$\mathrm{Na}+C+N\to \mathrm{NaCN}$
2. Sulfur reacts with sodium to form sodium sulfide:
$2\mathrm{Na}+S\to {\mathrm{Na}}_{2}S$
3. Halogens (X = Cl, Br, I) react with sodium to form sodium halides:
$\mathrm{Na}+X\to \mathrm{NaX}$

The reaction:
$2\mathrm{CuO}+C\to 2\mathrm{Cu}+{\mathrm{CO}}_2$
represents the reduction of copper(II) oxide by carbon. This reaction is part of the test used to detect carbon (and hydrogen) in an organic compound (often referred to as the Copper Oxide Test), where the organic compound is heated with copper(II) oxide to oxidize carbon to carbon dioxide. It does NOT belong to Lassaigne's test.