Answer
a. $HNO_3$ is a strong acid.
b. $HCl$ is a strong acid.
c. $HBr$ is a strong acid.
d. $H_2S{O_3}$ is a weak acid. $$K_a = \frac{[HS{O_3}^-][H_3O^+]}{[H_2SO_3]}$$
Work Step by Step
If the acid is on the "Strong Acids" table (Table 16.3, page 729), it is a strong acid; if the acid does not appear on this list, it is probably a weak acid.
d.
1. Write the balanced equation for the ionization of this acid:
$$H_2SO_3(aq) + H_2O(l) \leftrightharpoons HS{O_3}^-(aq) + H_3O^+(aq)$$
2. The exponent of each concentration is equal to its balance coefficient.
$$K_a = \frac{[Products]}{[Reactants]} = \frac{[ H{SO_3}^- ][ H_3O^+ ]}{[ H_2SO_3 ]}$$
