Select the correct statement(s).

(A) is correct. $\mathrm{H_3PO_3}$ has two ionisable $\mathrm{O{-}H}$ groups and one $\mathrm{P{-}H}$, so it is dibasic; $\mathrm{H_3PO_2}$ has one $\mathrm{O{-}H}$ and two $\mathrm{P{-}H}$ bonds, so it is monobasic, and the $\mathrm{P{-}H}$ bonds make it reducing. (B) is wrong: boric acid is a monobasic Lewis acid, accepting $\mathrm{OH^-}$ to give $\mathrm{[B(OH)_4]^-}$ rather than losing three protons. (C) is correct: $\mathrm{NO}$ ($11$ valence electrons) and $\mathrm{NO_2}$ (odd electron) are paramagnetic, whereas the dimer $\mathrm{N_2O_4}$ has all electrons paired and is diamagnetic. (D) is wrong: with dilute nitric acid, zinc is oxidised mainly to $\mathrm{Zn^{2+}}$ with $\mathrm{N_2O}$ as the main reduction product (and $\mathrm{NH_4^+}$ with very dilute acid), while $\mathrm{NO_2}$ is the characteristic product with concentrated acid.