JEE Advanced 2021 · Paper 2 · Chemistry Q6

ChemistryMultiple correct+4 / -2Question 25 of 57

The correct statement(s) related to oxoacids of phosphorous is(are)

Upon heating,

\ce{H3PO3}

undergoes disproportionation reaction to produce

\ce{H3PO4}

and

\ce{PH3}

While

\ce{H3PO3}

can act as reducing agent,

\ce{H3PO4}

cannot.

\ce{H3PO3}

is a monobasic acid.

The H atom of P-H bond in

\ce{H3PO3}

is not ionizable in water.

Answer and worked solution

Official answer: A, B, D

Structure. $\ce{H3PO3}$ is $\ce{HPO(OH)2}$ : two P-OH groups and one P-H bond.

Check each option.

(A) On heating, $\ce{4H3PO3 -> 3H3PO4 + PH3}$ , a disproportionation. True.
(B) The P-H bond makes $\ce{H3PO3}$ a reducing agent. $\ce{H3PO4}$ (P at +5, no P-H) is not. True.
(C) Only the two OH hydrogens ionise, so $\ce{H3PO3}$ is dibasic, not monobasic. False.
(D) The P-H hydrogen does not ionise in water. True.

(A), (B), (D)

Topics:Oxoacids Group 15 Oxidation number

JEE Advanced 2021 · Paper 2, Chemistry question 6