If a small amount of a strong base is added to buffer made up of a weak acid, HA, and the sodium salt of its conjugate base, NaA, the pH of the buffer solution does not change appreciably because:- a. CH3COOK or NaOH
b. CH3COOK only
c. NaOH only
d. NH4Cl only
e. NaCl or CH3COOK

Explanation is in the answer

Explanation:

The pH of the buffer solution does not change appreciably because the strong acid (free H⁺) reacts with conjugate base of buffer producing more weak acid. pH formula of buffers is (Henderson-Hasselbalch formula):

pH = pKa + log ( [A⁻] / [HA] )

The addition of strong acid decreases [A⁻] increasing [HA]. pH change just in the log of the ratio of [A⁻] with [HA], that is a real little effect over pH of the buffer solution.