Here's why:

* NaCl is a salt of a strong acid (HCl) and a strong base (NaOH). It completely dissociates in water, meaning it breaks down into its ions (Na⁺ and Cl⁻) almost entirely. This means its Kₐ is extremely high, practically infinite.

* CH₃COONa is a salt of a weak acid (CH₃COOH, acetic acid) and a strong base (NaOH). It undergoes partial hydrolysis, meaning it doesn't dissociate completely in water. The acetate ion (CH₃COO⁻) reacts with water to form acetic acid (CH₃COOH) and hydroxide ions (OH⁻). This reaction results in a lower Kₐ compared to NaCl.

Key Point: The dissociation constant is a measure of the extent to which a compound dissociates in solution. Salts of weak acids and strong bases have higher Kₐ values than salts of strong acids and strong bases.