Solution of a weak acid and its anion (that is,its conjugate base) or of a base and its common cation are buffered. When we add a small amount of acid or base to any one of the, the pH of solution change very little. pH of buffer solution can be computed as for acidic buffer : `pH=pK_(a)+ log.(["Conjugate base"])/(["Acid"])`
for basic buffer : `pOH=pK_(b)+log.(["Conjugate acid"])/([Base])`
It is generly accepted that a has useful buffer cpacity (pH change resisting power) provided that the value of [salt or conjugate base] /[acid] for acidic buffer lies within the range of 1 : 10 to 1. Buffer capacity is maximum when [conjugate base] = [acid]
one litre of an aqueous solution contains 0.15 mole of `CH_(3)COOH(pK_(a=4.8))` and 0.15 mole of `CH_(3)` COONa. After the addition of 0.05 mole of solid NaOH to this solution, the pH will be :

Options

A. 4.5
B. 4.8
C. 5.1
D. 5.4