Question

Write the chemical formula of the following compound in a step-by-step manner –

Iron [III] oxide

Answer 1

Write the formula of

Iron [III] oxide	Symbol	Valency
Iron	\[\ce{Fe}\]	\[\ce{3^{+}}\]
Oxide	\[\ce{O}\]	\[\ce{2^{-}}\]

Step I – Write each symbol with its valency.
Positive ion is written first
\[\ce{Fe}^{3+}\]  \[\ce{O}^{2-}\]
Step II – Interchange the valencies ignoring (+) and (−) signs.

The Formula is \[\ce{Fe2O3}\]