Which buffer solution out of the following will have $pH > 7$?
(A) $C{H_3}COOH + C{H_3}COONa$
(B) $HCOOH + HCOOK$
(C) $C{H_3}COON{H_4}$
(D) $N{H_4}OH + N{H_4}Cl$

Hint: An aqueous solution which consists of a mixture of a weak acid and its salt or a weak base with its salt is known as a buffer. The $pH$ of a buffer changes very less when a little amount of strong base or strong acid are added to it. So, because of this reason a buffer is used to prevent the $pH$ change of a given solution.

Complete Step by Step Solution:
The solutions having a stable concentration of hydrogen ions and hence no change in $pH$ which is independent of dilution and also which change very less with the addition of small amounts of strong acid or alkali are known as buffers. In simple terms, a buffer can be defined as a solution that prevents any change in $pH$ whenever a small amount of a strong base or strong acid is added to the solution. A basic buffer is a buffer solution that has relatively large quantities of a weak base and its salt with a strong acid. The $pH$ of these buffers is more than $7$ at the temperature of $298K$. A good example of a basic buffer is $N{H_4}OH + N{H_4}Cl$.
Therefore, option D is the correct answer.

Note: In any chemical reaction, the acidity of the solution in which they occur affects so much. The $pH$ of the reaction medium should be controlled for a chemical reaction to take place or to take place at a suitable rate. This control is often provided by buffer solutions, which are solutions that usually preserve a certain $pH$.