Among $CO_3^{2-}$,$OH^{-}$,$NH_3$ and $HCO_3^{-}$,the species that acts as a Bronsted acid as well as a Bronsted base,is

An acid is a compound which furnishes ($Bronsted-Lowry$ concept):

Which of the following cannot act as a Bronsted base?

In the reaction $2H_2O \rightleftharpoons H_3O^{+} + OH^{-}$,water is

$K_{a}$ values for acids $H_{2}SO_{3}$,$HNO_{2}$,$CH_{3}COOH$ and $HCN$ are respectively $1.3 \times 10^{-2}$,$4 \times 10^{-4}$,$1.8 \times 10^{-5}$ and $4 \times 10^{-10}$. Which of the above acids produces a stronger conjugate base in aqueous solution?

When hydrogen chloride is dissolved in acetic acid,the following equilibrium is established: $HCl + CH_3COOH \rightleftharpoons Cl^- + CH_3COOH_2^+$. Identify the conjugate acid-base pairs.