This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Enzymes, Subject name: Biochemistry
When the pH of a solution of a weak acid, HA, is equal to the pKa, the ratio of the concentrations of the salt and the acid (/) is which one of the following? 
Select and explain. 
A. 0, B. 1, C. 2, D. 3
B: 1
Answer: B: 1 
Explanation: The pKa is the pH at which the functional group is 50% dissociated, which in this case is the pH at which = The Henderson-Hasselbalch equation, pH=pKa +log10/, gives the relationship between these parameters. If pH=pKa , log10/=0,and/=1