One of your non-Chemistry teachers mentions a compound called ethylmethane. There is no such named compound. A structure that looks like it could be called ethylmethane would actually be called:

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.

the answer is d.) potassium