(s) about p-block compounds.

(A) Correct. Only the $\mathrm{P-OH}$ hydrogens are ionisable: $\mathrm{H_3PO_3}$ has two $\mathrm{P-OH}$ groups and one $\mathrm{P-H}$ (dibasic); $\mathrm{H_3PO_2}$ has one $\mathrm{P-OH}$ and two $\mathrm{P-H}$ (monobasic). (B) Incorrect. $\mathrm{XeF_4}$ has four bond pairs and two lone pairs on xenon ($sp^3d^2$), giving an octahedral electron geometry and a square planar shape. (C) Incorrect. $\mathrm{HF}$ boils at $293\ \mathrm{K}$ against $188\ \mathrm{K}$ for $\mathrm{HCl}$ because of extensive hydrogen bonding; molecular mass is not decisive here. (D) Incorrect. Back donation from the halogen lone pair into the empty $2p$ orbital of boron is better for the smaller, more compact $3p$ orbital of chlorine than for the diffuse $4p$ of bromine, so $\mathrm{BCl_3}$ is the weaker acid of the two (the claim reverses the real order); the Lewis acidity order is $\mathrm{BBr_3}>\mathrm{BCl_3}>\mathrm{BF_3}$.