Answer the question on the basis of the passage given below:
Oxides formed by \(p\)- block elements are acidic, basic and neutral. Also, elements of \(p\)-block form different acids.
Match List I with List II
| List I Oxides | List II Oxidation state |
| A. \(H_4P_2O_7\) | I. +1 |
| B. \(H_4P_2O_6\) | II. +3 |
| C. \(H_3PO_2\) | III. +4 |
| D. \(H_3PO_3\) | IV. +5 |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-IV, B-III, C-I, D-II
The oxidation state of phosphorus in an oxoacid is found from the charge balance: H is +1, O is −2, and the molecule is neutral.
(A) \( \ce{H4P2O7} \) (pyrophosphoric acid) — This matches (IV) +5: 4(+1) + 2x + 7(−2) = 0 gives 2x = 10, x = +5.
(B) \( \ce{H4P2O6} \) (hypophosphoric acid) — This matches (III) +4: 4(+1) + 2x + 6(−2) = 0 gives 2x = 8, x = +4.
(C) \( \ce{H3PO2} \) (hypophosphorous acid) — This matches (I) +1: 3(+1) + x + 2(−2) = 0 gives x = +1.
(D) \( \ce{H3PO3} \) (phosphorous acid) — This matches (II) +3: 3(+1) + x + 3(−2) = 0 gives x = +3.
Shortcut: (C)-(I) leaves Options (2) and (4); (D)-(II) leaves only Option (2).
Note 1: It seems that there is a mistake in the original NTA paper. The heading of List I reads “Oxides”, but the four compounds listed are oxoacids of phosphorus.
Note 2: 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 – …
