It does, in fact, have to do with levels. The PH of an acid tells how reactive it is. The concentration of the acid is also very important. Citric acid is faily acidic, but there is a small amount in fruit. Fortunately, people don't hold these liquids in their mouths for days on end, and saliva has a neutralizing effect as well.
Sublimation is when a solid changes to a gas or when a gas changes to a solid.
I hope that makes things less confusing for you. Ml stands for milliliter, and mg is milligrams. A milliliter is a measure of volume, or how much space something takes up. It is usually used when measuring a liguid, like water. A milligram is a measure of mass, or how much substance there is.