JEE Advanced · 2021 · 03 Oct 2021 · Paper 2 · p-Block Elements

${\mathrm{H}}_3{\mathrm{PO}}_3$ (phosphorous acid) has the structure with one P–H bond and two P–OH bonds, making it dibasic (two ionizable H atoms from OH groups), not monobasic. (A) Correct: $4{\mathrm{H}}_3{\mathrm{PO}}_3\stackrel{\Delta }{\to }3{\mathrm{H}}_3{\mathrm{PO}}_4+{\mathrm{PH}}_3$ is a disproportionation reaction. (B) Correct: ${\mathrm{H}}_3{\mathrm{PO}}_3$ has P in +3 oxidation state and can be oxidized (reducing agent), while ${\mathrm{H}}_3{\mathrm{PO}}_4$ has P in +5 (highest oxidation state) and cannot act as a reducing agent. (C) Incorrect: ${\mathrm{H}}_3{\mathrm{PO}}_3$ is dibasic. (D) Correct: The H directly bonded to P (P–H) is not ionizable in water; only the H atoms in OH groups are ionizable.