Answer:
160 mL of fruit juice and 400 mL of sparkling water
Explanation:
According to the statement we have that the ratio between fruit juice and sparkling water is 2/5. 
Therefore, we could also say that: 
200/500 
with it could be done with 200 mL of fruit juice and 500 mL of sparkling water, so for 400 mL, how much would it be: 
400 * 200/500 = 160 
Therefore, the largest amount of the drink can be made with 160 mL of fruit juice and 400 mL of sparkling water.