Answer:
Answer: a) 20g of H2O (18.02 g/mol) molecules=6.68x10^23
Explanation:
In order to find the amount of molecules of each of the options, we need to follow the following equation.

So, let´s get the number of molecules for each of the options.





the smalest number is in option a)
Best of luck.
http://century.rochester.k12.mn.us/cms/One.aspx?portalId=3086882&pageId=6133921
Hope this helps!
Please mark brainliest. :)