A student standardizes a solution of `Na_(2)S_(2)O_(3)` by titrating it against a solution containing a known mass of `NaIO_(3)` that has been dissolved in an excess of a freshly prepared solution of KI in dilute HCI. Which of the following errors will lead to a value of the molarity of the thiosulphate solution that is higher than the true value?
A. The student overshoots the endpoint of the titration
B. The `NaIO_(3)` is contamined with `NaCI`
C. The `KI//HCI` solution is allowed to stand overnight before it is used in the titration
D. The sample of sodium thiosulphate pentahydrate used to make the `Na_(2)S_(2)O_(3)` solution had partially dehydrated on standing
