Question

Balance H2 + O2 - H2O

Answer 1

The answer is:
  H2+1/2 o2-H2o

Answer 2

Currently in this equation, you have 2 hydrogen atoms and 2 oxygen atoms on the left, and then 2 hydrogen atoms and 1 oxygen atom on the right. To balance, you would need to even out the oxygens, so we can first place a 2 in front of H2O to get:
H2 + O2 -> 2H2O

Now, however, you can see that we have too many hydrogen atoms on the right, so to get the final answer, we add a 2 in front of hydrogen on the left:

2H2 + O2 -> 2H2O

I hope this helps!