#### Answer

a. $H_2O$ is the stronger base;
b. $N{O_2}^-$ is the stronger base;
c. $OC_6{H_5}^-$ is the stronger base;

#### Work Step by Step

- Identify the base with the weakest conjugate acid; it will be the stronger base.
Using the table 13-2, from page 531, and knowing that:
Strong acids: $K_a > 1$
$H_3O^+$: $K_a = 1.0$
a. $HCl$ has $K_a > 1$
$H_3O^+$ has $K_a = 1$
Therefore, $H_3O^+$ is the weaker acid, and $H_2O$ is the stronger base.
b. $H_3O^+$ has $K_a = 1$
$HNO_2$ has $K_a = 4.0 \times 10^{-4}$
Therefore, $HNO_2$ is the weaker acid, and $N{O_2}^-$ is the stronger base.
c. $HCN$ has $K_a = 6.2 \times 10^{-10}$
$HOC_6H_5$ has $K_a = 1.6 \times 10^{-10}$
Therefore, $HOC_6H_5$ is the weaker acid, and $OC_6{H_5}^-$ is the stronger base