(b) N2O4
(a) Iron (ii) chloride
Iron has two possible ions Fe2+ and Fe3+. Since it takes two chlorines (Cl-) to balance the iron, it can be assumed it is Fe2+, thus the name iron (ii). The anion of the compound ends with -ide, thus chlorine changing into chloride. Prefixes are not necessary for ionic compounds.
(b) Dinitrogen tetroxide
This is a molecular compound, which means prefixes are necessary. There are two nitrogens, so the prefix di- is used, and four oxygens, hence the prefix tetra-. Also, the second element ends with -ide.
(a) FeCl2
(b) N2O4
