Question

When the equation Fe + O2→Fe2O3 is balanced, the coefficient for O2 is:

Answer 1

B.) Balanced equation is : 4Fe + 3O2 ---> 2Fe2O3. So coefficient for O2 is 3.

Answer 2

The fully balanced equation would be 

4Fe + 3O2 --> 2Fe2O3

for each side, we have

4 Fe (4 iron)
6 Oxygen (O)

So the final answer is choice B) 3