This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Physiology
Plasma osmolarity is maximally affected by- 
Select and explain. 
A. Na+, B. K+, C. Glucose, D. Urea
A: Na+
Answer: A: Na+ 
Explanation: Ans. is 'a' i.e., Na+ * Normal osmolarity of (extracellular) body fluids is about 290 mOsm/L.* Important contributors of body fluid osmolarity areConstituentConcentration mMole/LNa+135-155Cr90-110HCO3-25K+3[?]5 - 5[?]0Glucose34 - 5[?]6 mmole/L (60-100 mg/dl)BUN3[?]6 - 7[?]1 mmole/L (10-20 mg/dl)