Answer: The chemical formula of the compound is

Step-by-step explanation:
Iron (III) phosphide is a compound which is formed by the combination of iron ion
and phosphide ion

The oxidation state of iron in the compound is +3 and the oxidation state of phosphorus in the compound is -3.
Thus, by criss-cross method, the oxidation states of the opposite ions becomes the subscipt of the other atom that represents the number of individual atoms in a compound. So, the chemical formula of iron (III) phosphide becomes

Hence, the chemical formula of the compound is
