What is (aq),(I), and (g) mean in H2O2(aq) -> H2O(l) + O2(g) and why is it nesesary to have (aq),(I), and (g)

Explanation:

A matter can be present in different states like solid, liquid or gas. When we write a chemical equation then states of species involved are also mentioned.

This is because it tells in what state the reactants were present and in what state the products are then formed.

For example,

Now here, (aq) means aqueous, (l) means liquid and (g) means gas.

So, these states denoted are necessary as it tells that in aqueous state dissociates to give in liquid state and in gaseous state.