This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Bio-Chemistry), Subject name: Biochemistry
In plasma, if pH is 5 , what is the fraction of base to acid? 
Select and explain. 
A. 0.01, B. 0.1, C. 1, D. 10
B: 0.1
Answer: B: 0.1 
Explanation: Ans: b (0.1)Ref: Vasudevan 4th ed/p.347According to Henderson-Hasselbach equation,pH = pKa + log (pKa= pH at which the acid is half ionised. It is a constant)The most important buffer system in plasma is bicarbonate- carbonic acid system. pKa for carbonic acid is 6.1 .pH = pKa + log rbasel5 = 6.1 + log log rbasel = -1.1 = log 10'-1 approx.