The first solution will be an unbuffered sucrose solution. Calculate the amount of 0.1 M sucrose stock solution and the amount of dH2O needed to prepare 100 mL of unbuffered 20 mM sucrose.

20mL of the stock solution and dilute to 100mL

Explanation:

20mM = 0.020M is the concentration of the diluted solution. As you want to prepare this solution from a 0.1M solution, dilution factor is:

0.1M / 0.020M = 5

That means you need to dilute the stock solution 5 times to obtain the 20mM sucrose solution.

As you want to prepare 100mL, you need to add:

100mL / 5 =

20mL of the stock solution and dilute to 100mL