Initial volume V1 = 400 µL
Initial molarity M1 = 6.67 * 10^-5
Final volume V2 = ?
Final molarity M2 = not given.
Some data is missing, since when we add the Ab to prepare solution we need to have the final molarity (since we should know how much amount of Ab should be added to make up to that concentration).
the question should be...
We have 1 ml of Ab and from that we are using 400 µL to prepare a solution of molarity say 10M so what will be the final volume?
If you add 1 mL + the 400 microliters the answer will be 1.400 mL. First you need to convert the 400 microliters to microliters to mL which is .400 mL because you move the decimal place three places to the left. The solution will only increase by .4 for the total volume is 1.4mL. Divide the volume by the molar mass to get the final concentration.