Answer : The volume range in milliliters for the solution is 0.25 - 0.5 mL
Explanation :
We have been given that there are approximately 20 drops per milliliter of water
This information can be used as a conversion factor as

We are using 5-10 drops of the solution.
Let us calculate milliliters in 5 drops.

Similarly, 10 drops would contain
solution.
Therefore the volume range in milliliters for the solution is 0.25 - 0.5 mL