Explanation:

A buffer is an aqueous solution that can resist significant changes in pH levels upon the addition of small amount of acid or alkali. Each buffer is characterized by a set ‘capacity’ which is defined as the quantity of strong acid or base that must be added to change the pH of one liter of solution by one pH unit. In other words, buffer capacity is the amount of acid or base that can be added before the pH begins to change significantly.

A buffer range is the specific pH range in which a buffer effectively neutralizes the added acid or base, while maintaining nearly constant pH. Capacity and range of a particular buffer ensures that the added small amount of acid/base is neutralized and the chemical reaction keeps going without giving a wrong outcome for the experiment/process. Simply put, a buffer is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.