PCl3
PCl3 is the formula. This is the compound we know as phosphorus trichloride.
C21H21O4P
Do you mean Boron Trichloride? BCl3 The formulae generally can be answered by looking at it's name Boron - the symbol for boron is B, Tri- means three, Chloride- Refers chlorine(Cl) Boron = B Chlorine = Cl
The chemical formula for trichloronitrobenzene is C6H2Cl3NO2.
C3O2 , also called Carbon Suboxide is the chemical formula for tri-carbon dioxide.
The name would be phosphorous tri-iodine
IF it existed it would be CN3. There is a compound C3N4
The chemical formula for Xenon Trioxide is XeO3 because the tri means 3 oxides to every Xenon.
ClF3 The tri- indicates that there are three atoms of fluorine in the compound.
The correct chemical formula for hepta boron triiodide is B7I3.
1-1-1 Tri-Chloro-Ethane
The name tells you the formula. Di- means 2, and tri- means 3, so the formula is S2O3.