Determine the number of H atoms in 3.26 g of water.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

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.

a is the correct answer