Which of the following synthetic chemical is responsible for ozone layer depletion?

Chlorofluorocarbons

The correct answer is option 2. Chlorofluorocarbons.

Chlorofluorocarbons (CFCs) are synthetic chemicals that consist of carbon, chlorine, and fluorine atoms. They were once widely used in various industrial applications, including as refrigerants, solvents, propellants in aerosol sprays, and in the manufacture of plastic foams and other products. However, CFCs are notorious for their destructive impact on the ozone layer in the Earth's stratosphere.

Here's an explanation of why CFCs are responsible for ozone layer depletion:

1. Ozone Depletion: When CFCs are released into the atmosphere, they are eventually carried into the stratosphere, where they undergo photodissociation by ultraviolet (UV) radiation from the Sun. This process breaks down the CFC molecules, releasing chlorine atoms.

2. Chlorine Reaction:  Once released, chlorine atoms react with ozone \((O_3)\) molecules in the stratosphere. A single chlorine atom can catalytically destroy many ozone molecules in a chain reaction. The reaction proceeds as follows:
\[\text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2\]

\[\text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2\]

The net result of these reactions is the depletion of ozone molecules.

3. Ozone Layer Depletion: The depletion of ozone molecules in the stratosphere leads to the formation of an "ozone hole," particularly over the polar regions, during certain times of the year. This thinning of the ozone layer allows more harmful UV radiation from the Sun to reach the Earth's surface, increasing the risk of skin cancer, cataracts, and other health problems in humans, as well as damaging marine ecosystems and agricultural crops.

Due to the recognized environmental and health hazards associated with CFCs, their production and use have been significantly restricted under the Montreal Protocol, an international treaty aimed at protecting the ozone layer. Substitutes for CFCs, such as hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), have been developed as alternatives that have lower ozone-depleting potential.