Acetic Acid Is a Weak Acid That Dissociates into the Acetate

Acetic acid is a weak acid that dissociates into the acetate ion and a proton in aqueous solution:
HC₂H₃O₂ (aq) C₂H₃O₂^- (aq) + H⁺ (aq)
At equilibrium at 25 °C a 0.100 M solution of acetic acid has the following concentrations:
[HC₂H₃O₂] = 0.0990 M, [C₂H₃O₂^- ] = 1.33 × 10^{- 3} M, and [H⁺] = 1.33 × 10^{- 3} M. The equilibrium
Constant, K_eq, for the ionization of acetic acid at 25 °C is _ .

A) 5.71 × 10⁶
B) 1.75 × 10^{- 7}
C) 1.79 × 10^{- 5}
D) 5.71 × 10⁴
E) 0.100