Select the correct statement(s) about aqueous sodium hydrogencarbonate at 298 K.

AIts pH is close to the average of $p K_{a 1}$ and $p K_{a 2}$ of carbonic acid, about 8.3.
BWith excess $Ca (OH) X_{2}$ solution it gives a precipitate of $CaCO X_{3}$ .
CIt reacts with both dilute HCl and aqueous NaOH.
DIt is strongly alkaline with a pH of about 12.

Answer: A, B, C

HCO X_{3} X^{-}

is amphiprotic:

HCO X_{3} X^{-} + H X^{+} H X_{2} CO X_{3}

and

HCO X_{3} X^{-} + OH X^{-} CO X_{3} X^{2 -} + H X_{2} O

. Its pH is

\frac{1}{2} (6.35 + 10.33) \approx 8.3

, so it is weakly alkaline, not pH 12. With excess lime water,

HCO X_{3} X^{-} + OH X^{-} + Ca X^{2 +} CaCO X_{3} + H X_{2} O

precipitates. Three statements are correct.