Can anyone explain to me how to balance a chemical equation? im having trouble in understanding how i keep getting it wrong.

For example we are going to use this unbalanced chemical reaction:
H₂ + O₂ → H₂O.
First, calculate number of atoms (hydrogens and oxygens) on left and right. There is two oxygen and two hydrogen on left and two hydrogen and one oxygen on right.
You can not change molecular formula of compound, only you can put coefficient in fron of compound to balance reaction.
Put 2 in front water to balance oxygen (now you have two oxygens on left and right). But now you have four hydrogens on right, so you must put 2 in fron hydrogen on the left.
2H₂ + O₂ → 2H₂O.

To balance a chemical equation, one has to make the total number of molecules of each element equal on both sides of the equation.
 For example,
 in the reaction of sodium (Na) and chlorine (Cl2), we get sodium choride (NaCl)
 Na + Cl2--->NaCl
 Now one chlorine molecule contains 2 atoms of Cl and one Na molecule contains 1 atom of Na
 To balance, we have to take 2 Na molecules,
  2Na + Cl2 ---> NaCl
 Balancing both sides we get
 2Na + Cl2 = 2NaCl
 Here both sides of the chemical equation contains equal number of molecules of each element, so it is a balanced equation.

Elias is almost correct. he just got it backwards.the correct answer is that it demonstrates elastic potential energy transforming into kinetic energy.

What are the choices?