Which one is a Lewis acid?

Why is $K_{a_{2}} << K_{a_{1}}$ for $H_{2}SO_{4}$ in water?

The $CH_3COO^-$ ion is a.......

If $pK_b$ for fluoride ion $(F^-)$ at $25\,^{\circ}C$ is $10.83$,the ionisation constant $(K_a)$ of hydrofluoric acid $(HF)$ in water at this temperature is:

In the reaction $HCl + HF \rightleftharpoons H_2Cl^+ + F^-$,the behavior of the compound $HCl$ is......

$A$ substance containing hydrogen and releasing $H^{+}$ in aqueous medium is an acid. Identify the theory suggesting this concept from the following.