1. Types of Buffer Solutions:
• Acidic Buffer: Composed of a weak acid and its salt with a strong base.
• Basic Buffer: Composed of a weak base and its salt with a strong acid.
2. Evaluating the Options:
• (A) $HCl + NaCl$: $HCl$ is a strong acid. Strong acids do not form buffer systems because they dissociate completely and cannot provide the necessary equilibrium to resist $pH$ changes.
• (B) $CH_3COOH + CH_3COONa$: $CH_3COOH$ (Acetic acid) is a
weak acid, and $CH_3COONa$ (Sodium acetate) is its salt with a strong base ($NaOH$). This combination perfectly satisfies the criteria for an acidic buffer.
• (C) $CH_3COOH + NaCl$: While Acetic acid is weak, $NaCl$ is not its salt; it is the salt of a strong acid and a strong base. This will not act as a buffer.
• (D) $NH_4OH + NaOH$: Both are bases ($NH_4OH$ is weak, $NaOH$ is strong). A buffer requires a base and its corresponding salt, not two different bases.
Thus, the mixture of Acetic acid and Sodium acetate is the only correct buffer combination.