Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is

Grapes hanging on the plant do not ferment,but after being plucked from the plant,they can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

Explain,giving chemical equations,any two uses of chemical decomposition reactions in industry.

You could have noted that when copper powder is heated in a china dish, the surface of copper powder becomes coated with black coloured substance.
$(i)$ Why has this black coloured substance formed?
$(ii)$ What is this black substance?
$(iii)$ Write the chemical equation of the reaction that takes place.

Which of the following are combination reactions?
$(i) 2 KClO_3 \xrightarrow{\text{Heat}} 2 KCl + 3 O_2$
$(ii) MgO + H_2O \longrightarrow Mg(OH)_2$
$(iii) 4 Al + 3 O_2 \longrightarrow 2 Al_2O_3$
$(iv) Zn + FeSO_4 \longrightarrow ZnSO_4 + Fe$

Describe an activity to show a decomposition reaction in which light is used to decompose a reactant. Write the chemical equation of the reaction and state its one use.