An acid solution of pH = 6 is diluted 1000 times, the pH of the final solution  is

pH = 6 means H+   = 10-6 M. After dilution, the hydrogen ion concentration becomes 10-9 M. Under such conditions, the hydrogen ions obtained from water cannot be neglected.∴       Total H+   = 10-9 + 10-7 approx.=  10-7  10-2 + 1 = 10-7 1.01[The contribution of H+ from water will not be exactly 10-7  but still we can make an approximation in an objective problem and take it as 10-7 ]pH=-log H+ =-1.01 × 10-7 =7 - 0.0043 = 6.9957