Both oxygen helium and carbon dioxide are gasses. Also each of them is compressible<span>, which means that there is lots of free space between particles in oxygen helium and carbon dioxide. </span>
They are all elements that exist as gases by nadine.
The second group is the:
Option D. control group
This question seems like its too easy so i might have got it wrong.. but would't you just subtract 20 and 10 from 800 to get 770?
