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
[{'content': 'Which ion is essential in PCR \nSelect and explain. \nA. Ca+2, B. Cu+2, C. mg+2, D. 2n+2', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Magnesium is required as a co-factor for the enzyme Taq polymerase used in PCR.', 'role': 'assistant'}]