According to the Brönsted-Lowry concept, a protonic acid is a substance that is capable of donating a hydrogen ion ($\text{H}^+$) . Boric acid, $\text{B(OH)}_3$, is not a protonic acid because it does not donate protons directly on its own. Instead, it is an electron-deficient compound and acts as a Lewis acid by accepting an electron pair from the hydroxyl ion ($\text{OH}^-$) of a water molecule . This interaction releases a proton ($\text{H}^+$) from water into the solution: $\text{B(OH)}_3 + \text{2H}_2\text{O} \rightleftharpoons [\text{B(OH)}_4]^- + \text{H}_3\text{O}^+$. The other given compounds are protonic (Brönsted) acids as they have ionizable protons: $\text{PO(OH)}_3$ is Phosphoric acid ($\text{H}_3\text{PO}_4$) $\text{SO(OH)}_2$ is Sulphurous acid ($\text{H}_2\text{SO}_3$) $\text{SO}_2\text{(OH)}_2$ is Sulphuric acid ($\text{H}_2\text{SO}_4$).