Analyzing Environmental Statements

Let's carefully examine each of the given statements to determine their correctness in the context of environmental science.

Statement (a): Chlorofluorocarbons are responsible for ozone layer depletion.

This statement is widely accepted as true. Chlorofluorocarbons (CFCs) are synthetic organic compounds that were historically used in propellants, refrigerants, and solvents. When released into the atmosphere, they rise to the stratosphere where ultraviolet (UV) radiation breaks them down, releasing chlorine atoms. These chlorine atoms then act as catalysts to break down ozone ($\text{O}_3$) molecules, leading to the thinning of the ozone layer.

Therefore, statement (a) is correct.

Statement (b): Greenhouse effect is responsible for global warming.

The greenhouse effect is a natural process where certain gases in the Earth's atmosphere trap heat from the sun. These gases, known as greenhouse gases (GHGs), include carbon dioxide ($\text{CO}_2$), methane ($\text{CH}_4$), nitrous oxide ($\text{N}_2\text{O}$), and water vapor ($\text{H}_2\text{O}$). While the natural greenhouse effect is essential for keeping the Earth warm enough to support life, an increase in the concentration of GHGs due to human activities enhances this effect, leading to a gradual increase in the Earth's average temperature, which is known as global warming.

Therefore, statement (b) is generally considered correct as the enhanced greenhouse effect is the primary driver of anthropogenic global warming.

Statement (c): Ozone layer does not permit infrared radiation from sun to reach the earth.

This statement is incorrect. The ozone layer primarily absorbs harmful ultraviolet (UV) radiation from the sun, particularly UV-B. Infrared (IR) radiation, which is thermal radiation or heat, is largely transmitted through the atmosphere to the Earth's surface. It is greenhouse gases like $\text{CO}_2$ and $\text{H}_2\text{O}$ vapor that absorb and re-emit infrared radiation, causing the greenhouse effect.

Therefore, statement (c) is incorrect.

Statement (d): Acid rain is mostly because of oxides of nitrogen and sulphur.

This statement is correct. Acid rain is caused by atmospheric pollution from the emission of sulfur dioxide ($\text{SO}_2$) and nitrogen oxides ($\text{NO}_x$). These pollutants react with water molecules, oxygen, and other chemicals in the atmosphere to form sulfuric acid ($\text{H}_2\text{SO}_4$) and nitric acid ($\text{HNO}_3$). These acids then mix with rain and fall to the earth as acid rain.

Therefore, statement (d) is correct.

Summary of Statements

• Statement (a): Chlorofluorocarbons are responsible for ozone layer depletion. - Correct
• Statement (b): Greenhouse effect is responsible for global warming. - Correct
• Statement (c): Ozone layer does not permit infrared radiation from sun to reach the earth. - Incorrect (It absorbs UV radiation)
• Statement (d): Acid rain is mostly because of oxides of nitrogen and sulphur. - Correct

Based on the analysis, the correct statements are (a), (b), and (d).