A) In an experiment, a student needed to use a 0.25 M NaOH solution as standard solution. He prepared 250 mL of the working solution from a stock solution labeled as 50% NaOH. Despite knowing the concentration of the stock and working solutions, the student still needs to standardize the working solution. Give one property of NaOH that explains why the student is still required to standardize the working solution despite knowing he was preparing 0.25 M NaOH solution from the stock solution. Justify your answer. (2 marks)