Final answer:
The correct buffer system is B. H₂CO₃ (carbonic acid) and KHCO₃ (potassium bicarbonate). Hence, the correct answer is option B.
Step-by-step explanation:
The buffer system among the given options is B. H₂CO₃ and KHCO₃. A buffer is a solution that resists changes in pH upon the addition of small amounts of acid or base. Buffers are typically made from a weak acid and its conjugate base, or a weak base and its conjugate acid.
In this case, H₂CO₃ (carbonic acid) is a weak acid, and KHCO₃ (potassium bicarbonate) is a salt that provides the conjugate base, HCO₃- (bicarbonate ion). When small amounts of acid or base are added to this buffer system, the pH remains relatively stable.
The additional protons (H+) or hydroxide ions (OH-) are neutralized by the buffer components. This combination falls in line with the principle that strong acids and strong bases, such as HCl and NaOH, do not form buffers since they fully dissociate in water, leaving no weak conjugate partners to maintain the pH.