Question 3
What is the balanced equation for hydrogen reacting with oxygen to form water?
The right answer is the one marked above.
2H2 + O2 → 2H2O. Both sides have four hydrogen atoms and two oxygen atoms.
H2O2 is hydrogen peroxide, a different substance; changing a formula to even up the oxygen is wrong. And 4H2 gives eight hydrogens on the left against four on the right.