Titration Question Kaplan FL1

Hey all,

I have a question about number 15 from Kaplan FL1 chem/phys.

The question states: "A conservationist would like to test the acidity of a sample of rainwater by titrating it with 0.05M NaOH. What additional information is needed to the initial number of moles of H2CO3 in the sample?

I. Volume of NaOH used to reach the end point
II. Ka of H2CO3
III. Initial volume of rainwater in the sample

So, the answer states that choice II is not needed, which I do not understand. If the...

Titration Question Kaplan FL1