How does dilution affect the pH of basic solution?

Hint: We know that, the value of pH tells us the acidity or basicity of a solution. The pH measures the hydrogen ion concentration in a solution. It is the negative logarithm of hydrogen ions in a solution, that is, ${\text{pH}} = - {\text{log}}\left[ {{{\text{H}}^ + }} \right]$.

Complete step by step answer:
We know that dilution is the process in which water or any other solvent is added to the solution to decrease the concentration.
An acidic solution possesses more hydrogen ions than hydroxide ions and a basic solution has more hydroxide ion than hydrogen ion. Addition of water to an acidic or basic solution causes change of pH.
Let’s understand how pH changes when a basic solution is diluted. When an alkali solution is diluted, the concentration of hydroxide ions decreases. This results in the decrease of pH of alkali towards 7. This makes the solution less alkaline. That means the pH decreases on diluting an alkaline solution.

Additional Information:
Let’s discuss how pH changes when an acidic solution is diluted. When water is added to the acidic solution, the concentration of the hydrogen ions increases and this results in the increase of pH of the solution.

Note: It is to be remembered that pH scale is the range used for expressing the nature of any solution. We know that at 298 K, $\left[ {{{\text{H}}_{\text{3}}}{{\text{O}}^ + }} \right]$ ranges from ${10^0}\,{\text{M}}$ to ${10^{ - 14}}{\text{M}}$. The corresponding pH range is 0 t0 14. For a neutral solution, pH is equal to 7, for an acidic solution, pH is less than 7 and for a basic solution pH is more than 7.