Oh man! Well... uhh... 3.5 is half of 7... and that takes half of the height of the... I guess cylinder? hydrogen Dioxide would probably be... a gas comparing Carbon Dioxide? I'm guessing .5 gas since it's the same thing as 50%? Eh... I felt like trying to understand it and giving it a shot. I'm in high school... so I don't think I would know. XD
@Anjire: I don't get why you people are commenting on that part in particular when there are a bunch of other problems within the idiom. As far as I know, technobabble is just supposed to sound smart and complicated, when it's usually just a long nerdy way of saying something simple... =p Just like my idiom!
Hydrogen Dioxide sounds more real to me anyway. XP
I didn't want to complete your riddle for everyone but if you are asking if the glass is half full or half empty in a round about way, then the chemical name should reflect water h2o: dihydrogen oxide or one of the many others per my link.
Sorry, I try to avoid math if I can. It has been too long since I took Calculus III and the like. I get enough math setting up spreadsheets for online gaming MMO's.