Write and balance the chemical equation for the reaction between carbon monoxide, co(g), and oxygen to form carbon dioxide, co2(g). use only integers (not fractions) and be sure to include the states of matter.

The Original equation for this reaction is:
CO + O2 → CO2
this is not a balanced equation.
as the reactants C = 1 and O= 3
and the products C= 1 and O=2
so we put 1/2 O2 instead of O2 to balance the no. of O atom on
 each side.
CO + 1/2 O2 → CO2 to get the integers number we will multiply by 2 
the final balanced equation is:
2CO(g) +O2(g) → 2CO2(g)
So we finally have 
at the reactants side C atom = 2 & O= 4
at the products side C atom = 2 & O = 4