State the law on which balancing is based. Then balance the skeletal equation for iron and steam, Fe + H₂O → Fe₃O₄ + H₂, step by step.

1. 1 · Define in one line. A balanced equation has the same number of atoms of each element on both sides.
2. 2 · Give the reason. It follows the law of conservation of mass: mass can neither be created nor destroyed in a reaction.
3. 3 · Balance step by step.
   • Balance O first: put 4 before H₂O.
   • Balance H: put 4 before H₂.
   • Balance Fe: put 3 before Fe.
4. 4 · Check and add state symbols. 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g). Fe 3, H 8, O 4 on each side.
5. 5 · Link to real life. Engineers use balanced equations to know how much air a burner, like an LPG stove, needs.
6. 6 · Close in one line. So balancing shows that atoms are only rearranged in a reaction.

Scoring tip: Show the atom count for each element on both sides. Examiners give a mark for the check line.