Some amount of hydrogen peroxide (H2O2) breaks down to produce 3 molecules of oxygen (O2) and 6 molecules of water (H2O). How many atoms of hydrogen are there?

The answer to the question is ;

By counting the number of hydrogen in the decomposed hydrogen peroxide, there are a total 12 atoms of hydrogen in the reaction.

Explanation:

To solve the question, we note that

6H₂O₂ (l) → 6H₂O (l) + 3O₂ (g)

From the stoichiometry of the reaction, as it can be seen by balancing the equation that 6 moles of hydrogen peroxide liquid decomposes to produce 6 moles of liquid water molecule (H₂O) and 3 moles of oxygen gas molecules O₂.

Therefore, taking  count of hydrogen atoms in the reactant, there are 12 atoms of hydrogen atoms in the 6 molecules of hydrogen peroxide before the decomposition took place.