1. If 3 molecules of iron react, then 4 molecules of H2 should be produced (coefficients).
2. If 3 molecules of iron react, then 4 molecules of water are needed (coefficients).
3. The mole ratio of iron to water is 3:4 (coefficients).
4. If 3 molecules of iron react, then 4 molecules of H2 are produced, and therefore are involved in the reaction (coefficients).
