In the reaction of iron water shown below what coefficient must be placed before the iron to balance the reaction fe+4h2o fe3o4 + 4h2

Answer is: three.
Unbalanced chemical reaction: Fe+4H₂O → Fe₃O₄ + 4H₂.
Balanced chemical reaction: 3Fe+4H₂O → Fe₃O₄ + 4H₂.
In balanced reaction, there is three iron atoms on the left and on the right, eight hydrogen atoms and four oxygen atoms on both side of chemical reaction.