The oxoacid of phosphorus that is easily obtained from a reaction of alkali and white phosphorus and has two P-H bonds, is :

Solution

Chemistry ma’am · 3 steps

White phosphorus in hot alkali gives hypophosphite, and its parent acid H₃PO₂ carries two P–H bonds.

1. The reaction. White phosphorus heated with NaOH solution disproportionates. Part of it becomes phosphine and the rest becomes sodium hypophosphite, NaH₂PO₂.

   P₄ + 3NaOH + 3H₂O → PH₃ + 3NaH₂PO₂

2. Name the acid. The parent acid of hypophosphite is hypophosphorous acid, H₃PO₂. Its IUPAC-style name is phosphinic acid. In its structure, P is bonded to one =O, one -OH and two H atoms.

   Option	Formula	P–H bonds	From P4 and alkali?
   (a) Phosphonic acid	H₃PO₃	1	no
   (b) Phosphinic acid	H₃PO₂	2	yes, as NaH₂PO₂
   (c) Pyrophosphorous acid	H₄P₂O₅	2 (one on each P)	no
   (d) Hypophosphoric acid	H₄P₂O₆	0	no

3. So. Only phosphinic acid, H₃PO₂, meets both conditions. The answer is (b).

The idea to keep. In phosphorus oxoacids, every H on an -OH is ionisable and every H on P is not. H₃PO₂ has 2 P–H and is monobasic. H₃PO₃ has 1 P–H and is dibasic.

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