The species among the following,which can act as an acid and a base is

Review the equilibrium and choose the correct statement:
$HClO_4 + H_2O \rightleftharpoons H_3O^{+} + ClO_4^-$

Which of the following statements is $NOT$ correct?

The conjugate bases for $HCO_3^-$ and $NH_3$,respectively,are

Given the following $K_a$ values,determine which species is the strongest base: $HSO_4^- = 1.2 \times 10^{-2}$,$H_2PO_4^- = 6.3 \times 10^{-8}$,$HCO_3^- = 4.7 \times 10^{-11}$.

Which among the following is the strongest acid?