Hint: Decomposition reactions: A reaction in which one reactant breaks down into two or more products is known as decomposition reaction. It is generally represented as $AB \to A + B$ where, AB is the parent molecule i.e., reactant while A and B are the product molecules.
Complete answer:
Hydrogen peroxide is a chemical compound with formula ${H_2}{O_2}$. In its pure form, it appears as a pale blue liquid which is slightly more viscous than water. It is commonly used as an oxidizer, antiseptic and bleaching agent. It is the simplest peroxide molecule and is found in biological systems including the human body.
In the presence of light, it slowly decomposes and finally undergoes a decomposition reaction to form water and oxygen. The reaction takes place as follows:
$2{H_2}{O_2}\xrightarrow{{{\text{sunlight}}}}2{H_2}O + {O_2}$
The rate of decomposition increases with increase in temperature, concentration as the stability of ${H_2}{O_2}$ decreases under alkaline conditions. It can also be decomposed biologically by enzyme catalase. The decomposition of hydrogen peroxide is a highly exothermic reaction i.e., it liberates large amount of heat and oxygen which can be dangerous as spilling high concentration hydrogen peroxide on a flammable substance can cause an immediate fire.
Thus, we can conclude that when hydrogen peroxide is exposed to sunlight, the formation of water and oxygen is observed.
Note:
Remember that the decomposition of hydrogen peroxide in the presence of certain metal ions such as $F{e^{2 + }}$ or $T{i^{2 + }}$ results in the formation of free radicals such as hydroxyl radical $\left( {H{O^ \bullet }} \right)$ and hydroperoxyl radical $\left( {HO{O^ \bullet }} \right)$ which are used widely in the organic reactions as the reactive intermediates.
