NaClO₃ ⇒ NaCl + O₂ ⇒ unbalanced
1. O : left 3, right 2
give coefficient left 2, right 3
2NaClO₃ ⇒ NaCl + 3O₂
2. Na and Cl : left 2, right 1
give coefficient right 2
2NaClO₃ ⇒ 2NaCl + 3O₂ ⇒ balanced
