Answer is: A. Only the Fe is unbalanced.
Unbalanced chemical reaction: Fe₂O₃ + 3CO → Fe+ 3CO₂.
a) On the left side of the unbalanced chemical reaction there are:
1) two iron atoms (in Fe₂O₃).
2) six oxygen atoms (three in Fe₂O₃ and three in 3 molecules of carbon monoxide CO).
3) three carbon atoms (in 3 molecules of carbon monoxide; 3 · 1 = 3).
b) On the left side of the unbalanced chemical reaction there are:
1) one iron atom (Fe).
2) six oxygen atoms (in 3 molecules of carbon dioxide CO₂; 3 · 2 = 6).
3) three carbon atoms (in 3 molecules of carbon dioxide CO₂; 3 · 1 = 3).
