Buffering is maximum when

Ans: a (pH = pKa) Ref: Vasudevan 4'k ecU p.346At values close to pKa, the buffer solution resists changes in pH most effectively. Buffering is the tendency of a solution to resist a change in pH more effectively after addition of a strong acid or base tha n does equal volume of water. Solutions of weak acids and their conjugate bases, and vice versa exhibit buffering. Strong acid /bases do not have buffering quality as great as the weak acid/ bases. pKa refers to the pH at which the concentration of acid equals that of base.* At pH = pKa, the solution would contain acid and base in equal amounts, and therefore would resist a change most effectively in either direction.Note:-The effective range of a buffer is one pH unit higher or lower than pKa.