Which of the following oxoacids of phosphorus contains only one –OH group in its structure?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Hypophosphorous acid
In the oxoacids of phosphorus, the ionisable hydrogens are those of the P–OH groups; hydrogens bonded directly to phosphorus (P–H) are not ionisable.
Hypophosphorous acid, H3PO2 — one P=O, one P–OH and two P–H bonds; a monobasic acid.
Orthophosphorous acid, H3PO3 — one P=O, two P–OH and one P–H bond; dibasic.
Orthophosphoric acid, H3PO4 — one P=O and three P–OH bonds; tribasic.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.