Which balances the equation mg + o2 → mgo?

a: mg + 2o2 → 4mgo
b: 2mg + 2o2 → 2mgo
c: 2mg + o2 → 2mgo
d: 2mg + 2o2 → 4mgo

C: 2Mg + O2 → 2MgO

Explanation:

We see that the reaction written like this is balanced. In fact, the number of atoms of each reactant matches with the number of atoms of each product:

Mg: we have 2 atoms on the left, and 2 atoms on the right

O: we have 2 atoms on the left, and 2 atoms on the right

All the other choices are unbalanced because:

A: Mg + 2O2 → 4MgO --> we have 1 atom of Mg on the left and 4 atoms of Mg on the right

B: 2Mg + 2O2 → 2MgO --> we have 4 atoms of O on the left and only 2 on the right

D: 2Mg + 2O2 → 4MgO --> we have 2 atoms of Mg on the left and 4 on the right