If you add NaOH to a solution containing 0.25 M acetic acid, will the concentration of protons increase or decrease?

Concentration of protons will decrease

Explanation:

CH₃COOH + H₂O → CH₃COO⁻ + H₃O⁺

In a medium of water, acetic acid donates its proton to water, to increase the [H₃O⁺]

When we a add a strong base, like NaOH, this also dissociates as this:

NaOH → Na⁺ + OH⁻

As we are adding OH⁻, they will bond to H₃O⁺ so they be neutralized and they will produce water, that's why the [H₃O⁺] will decrease.

2H₂O ⇄ H₃O⁺ + OH⁻ Kw