Answer the question on basis of passage given below:
P block elements are placed in groups 13 to 18 of the periodic table. Their valence shell electronic configuration is \(ns^2\, \ np^{1-6}\). Group 16 of the p-block elements are known as the group of chalcogens having \(ns^2\, \ np^4\) as their general electronic configuration. They exhibit number of oxidation states but the stability of \(-2\) oxidation state decreases down the group. They are sometimes also known as group of chalcogens as the name is derived from the Greek word for brass and points to the association of sulphur and its congeners with copper. Their ionization enthalpy decreases down the group. Oxygen shows anomalous behaviour due to its small size and high electronegativity.
Match the oxidation state of phosphorus in the following compounds to their counter parts in List II
| List I | List II |
| A. \(H_3PO_2\) | I. +3 |
| B. \(H_4P_2O_6\) | II. +5 |
| C. \(H_3PO_3\) | III. +1 |
| D. \(H_3PO_4\) | IV. +4 |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A-III, B-IV, C-I, D-II
Take H as +1 and O as −2 and let the oxidation state of P be x; the sum over the molecule is zero.
(A) H3PO2 — This matches (III) +1. 3(+1) + x + 2(−2) = 0, so x = +1.
(B) H4P2O6 — This matches (IV) +4. 4(+1) + 2x + 6(−2) = 0, so 2x = 8 and x = +4.
(C) H3PO3 — This matches (I) +3. 3(+1) + x + 3(−2) = 0, so x = +3.
(D) H3PO4 — This matches (II) +5. 3(+1) + x + 4(−2) = 0, so x = +5.
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 (Table 7.5, columns)
| Name | Formula | Oxidation state of phosphorus |
|---|---|---|
| Hypophosphorous (Phosphinic) | H3PO2 | +1 |
| Orthophosphorous (Phosphonic) | H3PO3 | +3 |
| Pyrophosphorous | H4P2O5 | +3 |
| Hypophosphoric | H4P2O6 | +4 |
| Orthophosphoric | H3PO4 | +5 |
| Pyrophosphoric | H4P2O7 | +5 |
| Metaphosphoric | (HPO3)n | +5 |