The principal buffer present in human blood is:
- ACH₃COOH + CH₃COONa
- BNaH₂PO₄ + Na₂HPO₄
- CH₂CO₃ + HCO₃⁻
- DH₃PO₄ + NaH₂PO₄
Show answer and explanation
Correct answer: (c) H₂CO₃ + HCO₃⁻
Explanation
A buffer is a mixture of a weak acid and its salt (conjugate base) that resists a change in pH when a little acid or base is added.
The main buffer in blood is the carbonic acid–bicarbonate system (H₂CO₃ / HCO₃⁻). It keeps blood pH within about 7.35–7.45:
- extra acid (H⁺) is taken up by bicarbonate, forming carbonic acid;
- extra base is neutralised by carbonic acid.
The phosphate buffer (H₂PO₄⁻ / HPO₄²⁻) works mainly inside cells and in the kidneys. Acetic acid with sodium acetate is a laboratory buffer.