Option C — Assertion (A) is true, but Reason (R) is false.
Haemoglobin in RBCs is indeed the respiratory pigment in humans. However, haemoglobin has a high affinity for oxygen, not carbon dioxide. CO₂ is transported mainly in dissolved form in plasma.
The Assertion is correctly stated — haemoglobin is the respiratory pigment present in red blood cells (RBCs). The Reason is factually wrong: haemoglobin binds strongly to oxygen (and carries it to body cells); carbon dioxide is transported primarily dissolved in plasma, not bound to haemoglobin. Since R is false, option C is correct. Remember this distinction — a common exam trap.