Question

I

Solid iron(III) oxide is produced when hot iron filings are exposed to pure
oxygen gas.

Answer 1

The unbalanced equation is:
Fe(s) + O2(g) —> Fe2O3(s)

To balance oxygens, multiply O2 by 3 and Fe2O3 by 2.

Fe(s) + 3O2(g) —> 2Fe2O3(s)

Balance your iron by multiplying Fe by 4, since you have 4 Fe in the products now.

4Fe(s) + 3O2(g) —> 2Fe2O3(s)