Class 11th

An acidic buffer solution consists of a weak acid and its conjugate base (usually from a salt).
Let's analyze the options:
(A) Strong acid (HCl) and a neutral salt (NaCl). Not a buffer.
(B) 100 mL of 0.1M HCl (10 mmol) is mixed with 200 mL of 0.1M CH?COONa (20 mmol). The strong acid (HCl) will react completely with the conjugate base (CH?COONa):
HCl + CH?COONa → CH?COOH + NaCl
After reaction, we have (20-10) = 10 mmol of CH?COONa (conjugate base) and 10 mmol of CH?COOH (weak acid) are formed. This mixture of a weak acid and its conjugate base is an acidic buffer.
(C) 100 mL of 0.1M CH?COOH (10 mmol) and 100 mL of 0.1M NaOH (10 mmol). They will neutralize each other completely to form sodium acetate. No buffer remains.
(D) 100 mL of 0.1M CH?COOH (10 mmol) and 200 mL of 0.1M NaOH (20 mmol). All the weak acid will be consumed, leaving a solution of sodium acetate and excess strong base (NaOH). Not an acidic buffer.