Here's why:

* Fe represents the element iron.

* Cl represents the element chlorine.

* 3 indicates that there are three chlorine atoms for every one iron atom.

The Roman numeral "III" in the name "iron(III) chloride" tells us that iron has a +3 charge in this compound. Chlorine typically has a -1 charge, so three chlorine atoms are needed to balance out the +3 charge of the iron.