JEE Main 2021 · 27 July · evening · Single correct · +4 / −1
Which one of the following set of elements can be detected using sodium fusion extract?
- (a) Sulfur, Nitrogen, Phosphorous, Halogens
- (b) Phosphorous, Oxygen, Nitrogen, Halogens
- (c) Nitrogen, Phosphorous, Carbon, Sulfur
- (d) Halogens, Nitrogen, Oxygen, Sulfur
Answer and solution
Answer (a) Sulfur, Nitrogen, Phosphorous, Halogens
Solution
Chemistry ma’am · 3 steps
Sodium fusion turns N, S, P and halogens into ions you can test in water. C and O never appear.
- What fusion does. Fusing the organic compound with sodium metal breaks its covalent bonds. The hetero-atoms become water-soluble sodium salts, and their ions are then tested in the extract.
Element Form in the extract Test Nitrogen NaCN Prussian blue with FeSO₄, then Fe³⁺ and acid Sulfur Na₂S Violet colour with sodium nitroprusside Halogens NaX Precipitate with AgNO₃ after boiling with HNO₃ Phosphorus phosphate, PO₄³⁻ (fused with an oxidising agent such as Na₂O₂) Yellow precipitate with ammonium molybdate after boiling with HNO₃ Carbon, Oxygen no testable ion not detected this way - Carbon and oxygen. Carbon is detected separately, by heating with CuO so that CO₂ turns lime water milky. Oxygen has no direct test and is found by difference.
- So. Only (a) lists elements that are all detected in the sodium fusion extract: sulfur, nitrogen, phosphorus and halogens.
The idea to keep. Lassaigne's extract tests the hetero-atoms N, S, P and halogens. Carbon and hydrogen are tested by the CuO method, and oxygen is found by difference.
Answer from the NTA final answer key. Solution by PrepWiser.