Conjugate acid and conjugate base of $HCO_3^{-}$ are respectively

Which of the following statements is true?

At $25^{\circ} C$,$K_{a}$ of formic acid is $1.8 \times 10^{-4}$. What is the $K_{b}$ of $HCOO^{-}$?

According to the Bronsted-Lowry concept,an acid is a substance which:

$HCO_3^-$ is a conjugate acid of :-

Complete the following Acid-Base reactions and identify each reactant as an Acid or a Base:
$(i)$ $CH_3NH_2 + H_2O$
$(ii)$ $CO_2 + H_2O$
$(iii)$ $H_2PO_4^- + CO_3^{2-}$
$(iv)$ $NH_2NH_2 + H_2O$
$(v)$ $C_6H_6 + NO_2^+$
$(vi)$ $C_6H_6 + NH_2^-$