This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology and Reproduction, Subject name: Physiology
Which of the following is considered the active from of calcium: 
Select and explain. 
A. Ionised calcium, B. Albumin bound calcium, C. Phosphate bound calcium, D. Protein bound calcium
A: Ionised calcium
Answer: A: Ionised calcium 
Explanation: Ans. (a) Ionised calcium(Ref: Ganong, 25th ed/p.375)Free calcium or ionized calcium is responsible for all the important actions of calcium