Which of the following will decrease the pH of 50 ml solution of 0.01 M HCl?
50ml of a mixture of NaOH and Na2CO3 titrated with N10 HCl using phenolpthalein indicator required 50ml of HCl to decolourise phenolpthalein. At this stage methyl orange was added and addition of acid was continued. The second end point was reached after further addition of 10ml of N10 HCl. The amount of NaOH in the solution is: