Answer:
The answer to your question is Cr₂O₃ + 3Mg ⇒ 2Cr + 3MgO
Step-by-step explanation:
Data  
Unbalanced chemical reaction
 Cr₂O₃ + Mg ⇒ Cr + MgO
 Reactants Elements Products
 2 Cr 1 
 3 O 1
 1 Mg 1
Balanced chemical reaction
 Cr₂O₃ + 3Mg ⇒ 2Cr + 3MgO
 Reactants Elements Products
 2 Cr 2 
 3 O 3
 3 Mg 3
Now the reaction is balanced