Which one of the following set of elements can be detected using sodium fusion extract?

Step 1: What Can Sodium Fusion Extract Detect?

In Lassaigne's test, the organic compound is fused with sodium metal. The covalently bonded heteroatoms are converted to ionic sodium compounds in the extract:

| Element | Product | Detection | |---|---|---| | N | $\ce{NaCN}$ | Prussian blue with $\ce{FeSO4}$ | | S | $\ce{Na2S}$ | Violet with sodium nitroprusside | | Cl | $\ce{NaCl}$ | White ppt with $\ce{AgNO3}$ | | Br | $\ce{NaBr}$ | Pale yellow ppt with $\ce{AgNO3}$ | | I | $\ce{NaI}$ | Yellow ppt with $\ce{AgNO3}$ | | P | $\ce{Na3PO4}$ | Yellow ppt with $\ce{HNO3}$ + $\ce{(NH4)2MoO4}$ |

Step 2: What CANNOT Be Detected?

• Oxygen: Cannot form a distinct, stable sodium ionic compound from covalently bonded O. Na fusion does not give a specific test for O. $\ce{C=O}$ groups don't give a detectable product.
• Carbon, Hydrogen: These form $\ce{CO2}$ and $\ce{H2O}$ during fusion — no specific ionic test.

Step 3: Evaluate Each Option

| Option | Elements | Contains O? | Correct? | |---|---|---|---| | (a) Halogens, N, O, S | Yes — O included | ❌ (O not detected) | | (b) S, N, P, Halogens | No O | ✅ | | (c) P, O, N, Halogens | Yes — O included | ❌ | | (d) N, P, C, S | Yes — C included | ❌ |

Answer: (b) Sulphur, Nitrogen, Phosphorus, Halogens

Key Points to Remember:

• Oxygen CANNOT be detected by Lassaigne's test
• Carbon CANNOT be detected by Lassaigne's test
• Hydrogen CANNOT be detected by Lassaigne's test
• The four elements detectable: N, S, Halogens (Cl, Br, I), and P