Arrange the following molecules in the increasing order of number of \(P – OH\) bonds present in it
(A) \(H_4P_2O_6\)
(B) \(H_3PO_2\)
(C) \(H_3PO_4\)
(D) \(H_3PO_3\)
Choose the correct answer from the options given below
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → B < D < C < A
In the oxoacids of phosphorus, each P is tetrahedrally surrounded and has one P=O. The remaining bonds are P–OH, P–H or P–P. Only the hydrogens in P–OH bonds are acidic, so the basicity of the acid equals its number of P–OH bonds.
B. \( \ce{H3PO2} \) (hypophosphorous acid): one P–OH, two P–H, monobasic — first
D. \( \ce{H3PO3} \) (orthophosphorous acid): two P–OH, one P–H, dibasic — second
C. \( \ce{H3PO4} \) (orthophosphoric acid): three P–OH, tribasic — third
A. \( \ce{H4P2O6} \) (hypophosphoric acid): four P–OH and one P–P bond — last
Shortcut: \( \ce{H3PO2} \) (B) has the fewest P–OH bonds and \( \ce{H4P2O6} \) (A) the most; of the two options that start with B and end with A, only Option (2) puts \( \ce{H3PO3} \) (D) before \( \ce{H3PO4} \) (C).
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.
NCERT (Pre-rationalised edition, 2022-23):
Oxoacids of Phosphorus – …
