Which is the properly balanced equation for the process in which iron oxide (fe2o3) and carbon monoxide (co) react to produce iron (fe) and carbon dioxide (co2) gas?
a.
fe2o3 + co → fe + co2
b.
fe2o3 + 3co → 2fe + 3co2
c.
2fe2o3 + 3co → 2fe + 3co2
d.
3fe2o3 + co → 3fe + 2co2

B. Fe2O3 +3CO --> 2Fe + 3CO2 

Fe has 2, Fe2 ---> 2Fe
O has 6, O3 + 3O (3+3=6) ---> 3(O2)(3x2=6) 
C has 3, (3C --> 3C) 

none of the other equations make sense:
In A, Fe on the left has 2 while Fe on the right has 1(so you can eliminate that.)
in C, Fe on the left has 4 (2x2) while Fe on the right has 2.(eliminate this too.)
in D, Fe on the left has 6 (3x2) and Fe on the right has 3 (eliminate this)