Question

What is the mole ratio of hydrogen and oxygen?

Answer 1

In this, the mole ratio that is asked for is the mole ratio of hydrogen and oxygen separated through the electrolysis of water. So the mole ratio should be found with respect to water and not any other compound.

Complete answer:
The mole ratio of hydrogen and oxygen is 2:1.
The mole ratio is the ratio of elements obtained by separation of a compound, here we have been asked for the mole ratio of hydrogen and oxygen, thus separation of basic compound water gives hydrogen and oxygen only.
This separation reaction is called a decomposition reaction in which the compound is decomposed into its elemental parts. There are mainly three types of decomposition reactions and electric decomposition reaction is one of them.
The decomposition of water is done by electrolysis decomposition reaction, in this water decomposes to give hydrogen at anode (positively charged) and oxygen at cathode (negatively charged).
The decomposition will stop at the equilibrium stage of the process, and hydrogen and oxygen will be in gaseous form. The reaction is shown below.
$2{{H}_{2}}O\to 2{{H}_{2}}+{{O}_{2}}$
In this reaction, as a water molecule breaks into hydrogen and oxygen, two hydrogen and two oxygen atoms will attach with each other to become stable. Thus, to get ${{O}_{2}}$ there has to be two water molecules, and as there becomes four hydrogen atoms, the ${{H}_{2}}$ becomes $2{{H}_{2}}$ .
Therefore, from this we can say that the mole ratio of hydrogen and oxygen is 2:1 as we get 2 moles of hydrogen and one mole of oxygen from electrolysis of water.

Note:
There are other methods for decomposition of compounds, such as thermal decomposition and photo decomposition reaction, but they cannot work for water as it will turn water into water vapour. Thus, the electrolysis method has to be used for decomposition of water.