% of iron by mass = 69.9 % [Given]
% of oxygen by mass = 30.1 % [Given]
Relative moles of iron in iron oxide:
\(=\frac{ \% \text{of iron by mass} }{ \text{Atomic mass of iron}}\)
\(= \frac{69.9 }{ 55.85}\)= 1.25
Relative moles of oxygen in iron oxide:
\(= \frac{\% \text{of oxygen by mass} }{ \text{Atomic mass or oxygen}}\)
\(= \frac{30.1 }{ 16.00}\)
= 1.88
Simplest molar ratio of iron to oxygen:
\(= 1.25\ratio 1.88\)
\(= 1\ratio 1.5\)
\(≈2\ratio 3\)
∴ The empirical formula of the iron oxide is \(\text{Fe}_2\text{O}_3\).