JEE Main · 2021 · 20 Jul 2021 · Shift 1 · p-Block Elements

Boric acid is purely acidic, and acidic in the Lewis sense: it does not release a proton of its own but accepts a hydroxide ion from water, $\mathrm{B}(\mathrm{OH}{)}_3+2{\mathrm{H}}_2\mathrm{O}\rightleftharpoons [\mathrm{B}(\mathrm{OH}{)}_4{]}^{-}+{\mathrm{H}}_3{\mathrm{O}}^{+}$, and it shows no basic behaviour at all. Aluminium hydroxide dissolves both in acid, giving $\mathrm{A}{\mathrm{l}}^{3+}$, and in alkali, giving the aluminate ion, so it is amphoteric. In each of the other sets the two members match in nature: ${\mathrm{H}}_3\mathrm{P}{\mathrm{O}}_3$ is an acid like boric acid, NaOH and $\mathrm{Ca}(\mathrm{OH}{)}_2$ are both strong bases, and $\mathrm{Be}(\mathrm{OH}{)}_2$ and $\mathrm{Al}(\mathrm{OH}{)}_3$ are both amphoteric. The set whose members differ in nature is $\mathrm{B}(\mathrm{OH}{)}_3$ and $\mathrm{Al}(\mathrm{OH}{)}_3$.