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.