This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which ion is essential in PCR 
Select and explain. 
A. Ca+2, B. Cu+2, C. mg+2, D. 2n+2
C: mg+2
Answer: C: mg+2 
Explanation: Magnesium is required as a co-factor for the enzyme Taq polymerase used in PCR.