Dear Student,
A buffer solution is a solution which resist changes in pH when small quantities of an acid or an alkali is added to it
Two main feature of buffer solution are as follows:
(a) The buffer functions most efficiently when its pKa is with in on unit of the the pH of the desired solution.
(b) Buffer capacity is defined as the ratio of weak acid to the conjugate base, Which should remain constant such that addition of acid or base does not change the pH of the solution