which equation is not balanced? A. 2H^2 O^2 arrow 2H^2O

You mean this?


2H_2 + O_2 \to 2H_2O


Count up the number of constituent atoms of each element on the left and right and see if they are equal. If they are, then the equation is balanced. For example on the left you have on oxygen molecule consisting of 2 atoms, and on the right you have two water molecules each with one oxygen atom, or two total. Hence the oxygen is balanced. Now check the hydrogen and let us know whether you think it's balanced.