Chapter 17.1, Problem 1CP

Which of the following would cause a decrease in the percent ionization of nitrous acid $\left(\text{HN}{\text{O}}_{\text{2}}\right)$ when added to a solution of nitrous acid at equilibrium? (Select all that apply.)

$\begin{array}{l}\text{a})\\ {\text{NaNO}}_{\text{2}}\\ \text{b)}\\ {\text{H}}_{\text{2}}\text{O}\\ \text{c)}\\ {\text{Ca(NO}}_{\text{2}}{\text{)}}_{\text{2}}\\ \text{d})\\ {\text{HNO}}_{\text{3}}\\ \text{e)}\\ {\text{NaNO}}_{\text{3}}\end{array}$