In the phase diagram the line between solid and liquid is where both phases available at the same time
Three is simply the coefficient which tells you the amount of molecules. In this case, there are three carbon dioxide molecules. If you want to break it down further, it also means there is three carbon atoms and six oxygen atoms.
I hope this helps.
Mutualism! The tree provides a home and food for the ants, while the ants protect the tree :)
