A is an aqueous solution of Acid and B is an aqueous solution of base. These are diluted separately. Then

When an acidic solution is diluted with water the concentration of $H^{+}$  ions decreases and pH of the solution increases towards 7.

Similarly when basic solution is diluted with water the concentration of $O{H}^{-}$  ions decreases, this causes the pH of the alkali to fall towards 7, making the solution less alkaline as more water is added.