This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid, Electrolyte, Subject name: Pediatrics
Maximum concentration of plasma calcium exist as - 
Select and explain. 
A. Complexed to phosphate, B. Complexed to citrate, C. Bound to plasma albumin, D. Ionized form
D: Ionized form
Answer: D: Ionized form 
Explanation: Plasma calcium exist as - 50 % - Biologically active ionized form 45% - Bound to plasma proteins (mainly albumin) 5% - Complexed to phosphate & citrate