What is Lassaigne's test?

Lassaigne's test (sodium fusion test) is used in organic chemistry to detect certain elements present in an organic compound by converting them into ionic sodium salts.

Elements detected by this test

On fusion with sodium:

• Nitrogen is converted into sodium cyanide, $\text{NaCN}$
• Sulphur is converted into sodium sulphide, $\text{Na}_2\text{S}$
• Halogens are converted into sodium halides, $\text{NaX}$
• Phosphorus can also be detected after fusion by converting it into sodium phosphate

Hence, Lassaigne's test is used for detecting: $\text{Nitrogen, Sulphur, Phosphorus and Halogens}$

Evaluate the options

• A: Phosphorous and halogens only — Incorrect, because nitrogen and sulphur are also detected.
• B: Nitrogen, Sulphur and Phosphorous only — Incorrect, because halogens are also detected.
• C: Nitrogen, Sulphur, phosphorous and halogens — Correct.
• D: Nitrogen and Sulphur only — Incorrect, because phosphorus and halogens are also detected.

Final answer

The correct option is: $\boxed{\text{C}}$