The reaction equation is:
FeCI₃ + MgO ---> Fe₂O₃ + MgCI₂
Balanced equation is the one in which the number of atoms of different elements in reactants is equal to the number of atoms of elements in products.
And when we balance the equation it will be;
2FeCI₃ +3MgO ---> 1Fe₂O₃ + 3MgCI₂