Oxoacids of phosphorus is/are correct?

One or more options correct

Which of the following statements about oxoacids of phosphorus is/are correct?

A. Hypophosphorous acid, $\mathrm{H_3PO_2}$ , is dibasic and has phosphorus in the $+3$ oxidation state
B. On heating, phosphorous acid, $\mathrm{H_3PO_3}$ , disproportionates into orthophosphoric acid and phosphine
C. In orthophosphoric acid all three $\mathrm{P\!-\!OH}$ groups are ionisable and phosphorus is in the $+3$ oxidation state
D. Pyrophosphoric acid, $\mathrm{H_4P_2O_7}$ , which contains a $\mathrm{P\!-\!O\!-\!P}$ linkage, is tribasic

Show answer and solution

Answer: B

\mathrm{H_3PO_2}

has structure

\mathrm{HPO(OH)H}

, i.e. one

\mathrm{P\!-\!OH}

and two

\mathrm{P\!-\!H}

, so it is monobasic, and the oxidation state of

\mathrm{P}

+1

(not

+3

); A is wrong. B:

4\,\mathrm{H_3PO_3}\xrightarrow{\Delta}3\,\mathrm{H_3PO_4}+\mathrm{PH_3}

, a disproportionation of

\mathrm{P}(+3)

into

\mathrm{P}(+5)

and

\mathrm{P}(-3)

; B is correct. C: the three

\mathrm{P\!-\!OH}

groups of

\mathrm{H_3PO_4}

are indeed ionisable, but phosphorus is in the

+5

state, so C is wrong. D:

\mathrm{H_4P_2O_7}

has four

\mathrm{P\!-\!OH}

groups (

\mathrm{(HO)_2P(O)\!-\!O\!-\!P(O)(OH)_2}

), so it is tetrabasic, not tribasic; D is wrong. Answer: B only.

Original question written in the JEE Advanced 2025 Paper 1 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake