Take 20 ml of the original solution and make up to the 100ml mark.
Using the dilution formula;
C1V1 = C2V2
C1 = concentration of the original solution
V1 = volume of original solution
C2 = concentration of new solution
V2 = volume of new solution
Now, the volume of the original solution that must be taken to prepare the new solution is V1;
V1 = C2V2/C1
V1 = 0.0400 × 100/0.200
V1 = 20 ml
Hence, you need to take 20 ml of the original solution and make up to the 100ml mark.
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