What is the pH of human blood?

✅ Correct Answer: C — 7.35 to 7.45

The normal pH of human blood ranges from 7.35 to 7.45, which is slightly alkaline (above neutral 7.0). The body has several buffer systems to maintain this narrow pH range, including the bicarbonate buffer system (primary), the phosphate buffer system, and the protein buffer system (hemoglobin acts as a buffer). The kidneys and lungs work together to regulate blood pH: the lungs control CO₂ levels (respiratory regulation) and kidneys control bicarbonate (metabolic regulation).

❌ Why other options are wrong:

• A. 6.4 to 6.8 — This range is acidic. Blood with this pH would indicate severe acidosis and would be incompatible with life. This is below the minimum survivable pH.

• B. 7.0 to 7.2 — This range is slightly acidic to neutral. While blood pH of 7.0-7.2 is above pure acid, it is still below the normal blood pH and would represent dangerous acidosis.

• D. 7.8 to 8.0 — This range is more alkaline than normal blood. pH above 7.45 causes alkalosis, and pH above 7.8 is life-threatening. This is not the normal range.

📝 Important Note: pH below 7.35 = Acidosis (respiratory or metabolic); pH above 7.45 = Alkalosis. Normal blood pH is maintained by bicarbonate buffer system (HCO₃⁻/H₂CO₃). The kidneys regulate blood pH by excreting or reabsorbing bicarbonate. This is a frequently tested SSC CGL Biology concept.