The correct answer is: B. Remains same.
A buffer solution is a solution that resists changes in pH when small amounts of acids or bases are added to it. This is because a buffer solution contains a mixture of an acid and its conjugate base, or a base and its conjugate acid. When an acid is added to a buffer solution, the conjugate base of the acid reacts with the acid to form more of the original acid. This prevents the pH of the solution from decreasing. When a base is added to a buffer solution, the conjugate acid of the base reacts with the base to form more of the original base. This prevents the pH of the solution from increasing.
The pH of a buffer solution is determined by the ratio of the concentrations of the acid and its conjugate base, or the base and its conjugate acid. The pH of a buffer solution is not affected by the volume of the solution. Therefore, if a buffer solution is diluted, the pH of the solution will remain the same.
Option A is incorrect because the pH of a buffer solution is not increased when the solution is diluted. Option C is incorrect because the pH of a buffer solution is not decreased when the solution is diluted. Option D is incorrect because the pH of a buffer solution does not slowly increase and then decrease when the solution is diluted.