WHO Oral Rehydration Solution (ORS) Composition

The World Health Organization's reduced-osmolarity Oral Rehydration Solution (ORS), which superseded the older formula, has a defined composition per litre designed to optimise sodium and water co-transport in the intestine while minimising the risk of hypernatremia.

Correct Composition

• Sodium (Na): 75 mmol/L (older standard formula: 90 mmol/L)
• Potassium (K): 20 mmol/L
• Chloride (Cl): 65 mmol/L (older standard formula: 80 mmol/L)
• Citrate: 10 mmol/L
• Glucose: 75 mmol/L
• Total osmolarity: 245 mOsm/L (reduced-osmolarity formula)
• Energy: approximately 54 kcal/L, derived mainly from the glucose content

Classic textbook descriptions of the original (pre-2002) WHO-ORS cite Na–90 mmol/L, K–20 mmol/L, Cl–80 mmol/L, with an energy content of approximately 54 kcal/L. This is the combination represented by option D (Na–90, K–20, Cl–80, Energy–54 kcal/L), which is the intended correct answer for this question.

Why the Other Options Are Incorrect

• Options A and B (Na–80, K–20, Cl–70, Energy–54 kcal/L): These are identical duplicate options and do not correspond to either the classic (Na 90/Cl 80) or the reduced-osmolarity (Na 75/Cl 65) WHO formulations; the sodium and chloride values are mismatched with recognised WHO figures.
• Option C (Na–90, K–40, Cl–80, Energy–27 kcal/L): The potassium value of 40 mmol/L is double the correct figure of 20 mmol/L, and the energy content of 27 kcal/L is far below the accepted value of about 54 kcal/L (which corresponds to the glucose load in the solution). Both values are inconsistent with the WHO formula.

Conclusion

The composition matching the classic WHO oral rehydration solution — Na–90 mmol/L, K–20 mmol/L, Cl–80 mmol/L, and Energy–54 kcal/L — corresponds to option D, making it the correct answer.