The number before is how many molecules and the small number is the amount of atoms in the molecules. with the 3 after the O means there is 3 and the 2 doubles everything. The small 2 after F means there are 2 F.
Recrystallization is the process in which a compound is dissolved in a hot solvent and then allowed to cool which forms the crystals.
It is a technique used for purification of solids.
Recrystallization mainly depends on the solubility of the solvent that means the solid should be soluble in the solvent when it is hot and should be insoluble in the same solvent when it is cool.
The observations while doing recrystallization is to observe the purified crystals obtained and to filter it out.