Which of the following is only acidic in nature?

$\mathrm{B}(\mathrm{OH})_3$ in aqueous medium coordinates a molecule of water to form the hydrated species
In this species, $\mathrm{B}^{3+}$ ion, because of its small size, exercises a high polarizing power thereby pulling the sigma electron charge of the coordinated $\mathrm{O}$ atom towards itself. The coordinated oxygen, in turn, pulls the sigma electron charge of the $\mathrm{OH}$ bond of the attached $\mathrm{H}_2 \mathrm{O}$ molecule towards itself. This facilitates the removal of $\mathrm{H}^{+}$ion from the $\mathrm{O}-\mathrm{H}$ bond, as shown below.
Thus the solution of $\mathrm{B}(\mathrm{OH})_3$ in water acts as a weak acid. That is why it reacts with $\mathrm{NaOH}$ solution to produce the sodium salt. $$ \begin{aligned} \mathrm{B}(\mathrm{OH})_3+\mathrm{NaOH} \rightleftharpoons & \rightleftharpoons \mathrm{Na}^{+}\left[\mathrm{B}(\mathrm{OH})_4\right]^{-} \\ \rightleftharpoons & \mathrm{Na}^{+} \mathrm{BO}_2^{-}+2 \mathrm{H}_2 \mathrm{O} \\ & \text { sodium } \\ & \text { metaborate } \end{aligned} $$