Concept:A buffer solution resists change in pH when a small amount of acid or base is added to it.
It is formed by mixing a weak acid with its salt of a strong base, or a weak base with its salt of a strong acid.
Explanation:In option A, acetic acid
CH3​COOH is a weak acid and sodium acetate
CH3​COONa is its salt formed with the strong base
NaOH.
This mixture provides both the weak acid
CH3​COOH and its conjugate base
CH3​COO− in solution.
The presence of both components lets the solution neutralise added acid or base, so it acts as an acidic buffer.
Option B does not contain the salt of acetic acid with a strong base.
Option C mixes a weak base with a salt of a strong acid and strong base, which is not a buffer pair.
Option D contains two weak acids only, so it cannot resist pH change.
Hence, only option A satisfies the buffer condition.
Answer:Option A: Acetic acid and sodium acetate.