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

The correct option is:
$2\mathrm{CuO}+C\to 2\mathrm{Cu}+\mathrm{CO}{2}_{}$

Step-by-Step Explanation:
Lassaigne's test (also known as the sodium fusion test) is a qualitative analysis method used to detect the presence of nitrogen (N), sulfur (S), and halogens (X = Cl, Br, I) in an organic compound.

During the test, the organic compound is fused with metallic sodium. This converts the covalently bonded elements (N, S, X) into water-soluble ionic sodium salts:
1. For Nitrogen: Sodium reacts with carbon and nitrogen from the organic compound to form sodium cyanide:
$\mathrm{Na}+C+N\to \mathrm{Na}\mathrm{CN}$
2. For Sulfur: Sodium reacts with sulfur from the organic compound to form sodium sulfide:
$2\mathrm{Na}+S\to {\mathrm{Na}}_{2}S$
3. For Halogens: Sodium reacts with halogens (represented by X) to form sodium halides:
$\mathrm{Na}+X\to \mathrm{Na}X$

The reaction:
$2\mathrm{CuO}+C\to 2\mathrm{Cu}+\mathrm{CO}{2}_{}$
represents the copper oxide test, which is used for the detection of carbon (and hydrogen) in an organic compound by oxidizing carbon to carbon dioxide. This reaction is not a part of Lassaigne's test.