Answer
a. $H_3O^+$ is stronger than $NH_4^+$
b. $HCl$ is stronger than $H_2SO_4$
c. $H_2CO_3$ is stronger than $H_2O$
Work Step by Step
Table 11.3 contains the relative strengths of these acids.
The acid strength increases from bottom to top. Therefore, if acid A is above acid B in this table, A is stronger than B.