2H₂O -> 2H₂ + O₂ is this equation balanced for White spheres represent hydrogen atoms, and red spheres represent oxygen atoms.

Yes, the equation is balanced. There are 4 hydrogen atoms on each side (2H₂ on the reactant side and 2H₂ on the product side) and 2 oxygen atoms on each side (2O on the reactant side and O₂ on the product side).