Answers 'a' a Roman numeral.
Fe(III)Cl3 - said as ' Iron three chloride'
This indictes that iorn is in oxidation state '3'.
Note that the oxidation numbr is always written after the element to which it refers, and is always in Roman Numerals.
Two more examples.
Fe(II)Cll2 - said as 'Iron two chloride'.
P(V)Cl5 = said as 'Phosphorus five chloride'.