When water is added to a basic solution, the number of hydroxide ions per unit volume decreases. What will be the effect on pH?

Correct answer: pH will decrease towards 7

For a basic solution, dilution lowers the hydroxide-ion concentration and reduces its basic strength. Because the ionic product of water relates hydrogen and hydroxide ions, the pH moves downward toward 7 as the solution is diluted, though it generally remains above 7 unless sufficient dilution or other conditions make it neutral. Thus option B is correct. Dilution cannot make the pH exceed 14, become zero, or immediately produce an acidic solution.