Answer:
D. [tex]K_{a} = \frac{[\text{H}^{+}][\text{NO}_{2}^{-}]}{[\text{HNO}_{2}]}[/tex]
Explanation:
The general form of an equilibrium constant expression is
[tex]K = \frac{[\text{Products}]}{[\text{Reactants}]}[/tex]
In the equilibrium
HNO₂ ⇌ H⁺ + NO₂⁻
The products are H⁺ and NO₂⁻, and the reactant is HNO₂.
∴ [tex]K_{a} = \frac{[\text{H}^{+}][\text{NO}_{2}^{-}]}{[\text{HNO}_{2}]}[/tex]
