Q.Solid (A) reacts with strong aqueous NaOH liberating a foul smelling gas (B) which spontaneously burns in air giving smoky rings. A and B are respectively

Step 1. Identify the reaction type.

A solid reacting with strong aqueous NaOH to liberate a foul-smelling gas that spontaneously catches fire in air, producing smoky rings, is a classic description of the reaction of white phosphorus with alkali.

Step 2. Write the reaction.

P4(white) + 3NaOH + 3H2O -> 3NaH2PO2 (sodium hypophosphite) + PH3(gas). This is a disproportionation: phosphorus in P4 (oxidation state 0) is both oxidised to +1 (in hypophosphite) and reduced to -3 (in phosphine).

Step 3. Confirm the gas's identity from its described behaviour. …

Match the described chemical behaviour (foul smell, spontaneous air-ignition with smoke rings) to the known laboratory preparation and …

Confusing this reaction with red phosphorus (which does not react this way with NaOH) or with …