Which one of the following compounds is not a protonic acid?

Which one of the following compounds is not a protonic acid?
  1. $\mathrm{B}(\mathrm{OH})_3$
  2. $\mathrm{PO}(\mathrm{OH})_3$
  3. $\mathrm{SO}(\mathrm{OH})_2$
  4. $\mathrm{SO}_2(\mathrm{OH})_1$

Solution

Boric acid is not a protic acid. Boric acid is a weak monobasic acid. It is not a protonic acid but acts as a Lewis acid by accepting electrons from a hydroxyl ion and in turn releases $\mathrm{H}^{+}$ ions Related Theory Although Boric acid contains $3 \mathrm{OH}$ groups yet it can act as monobasic acid rather than tribasic acid, since, only one $\mathrm{H}^{+}$can be released by a water molecule.

Asked in: NEET 2003

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