Heating white phosphorus with conc. NaOH solution gives mainly :

Solution

Chemistry ma’am · 3 steps

White phosphorus disproportionates in hot alkali: one P goes down to −3, the other three go up to +1.

1. Disproportionation. Phosphorus in P₄ has oxidation state 0, which sits between its lower and higher states. In hot concentrated NaOH, the same element is reduced and oxidised at the same time.

   P₄ + 3NaOH + 3H₂O →(Δ) PH₃ + 3NaH₂PO₂

2. Check the electrons. One P goes from 0 to -3 in PH₃ (phosphine), gaining 3 electrons. Three P go from 0 to +1 in NaH₂PO₂ (sodium hypophosphite), losing 3 × 1 = 3 electrons. Gain equals loss, so the equation is balanced.
3. So. The main products are PH₃ and NaH₂PO₂, which is option (d).

The idea to keep. When an element in oxidation state 0 meets hot alkali (like P₄, Cl₂ or S₈), expect disproportionation: one product with a lower oxidation state and one with a higher state.

Answer from the NTA final answer key. Solution by PrepWiser.