Which of the following is the weakest acid?

In the following reaction:
$[Al(H_2O)_6]^{+3} + HCO_3^{-} \rightleftarrows [Al(H_2O)_5OH]^{+2} + H_2CO_3$
$(A)\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad(B)\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad(C)\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad(D)$
Which species behave as Bronsted-Lowry acids?

Identify the conjugate base of ${H_2}PO_3^-$ and the conjugate acid of ${HCO_3^-}$.

The conjugate base of $NH_3$ is

Which acid is not an Arrhenius acid?

Which of the following is not a conjugate acid-base pair?