Question

The correct statement among the following is (a) Ozone layer is harmful when present in troposphere and protects life when present in stratosphere. (b) The industrial usage of fluorocarbons is very high because they can be manufactured cheaply. (c) Acid rains contain the oxoacids of sulphur and nitrogen. (d) All are correct.

Short answer

Statement (a) and (c) are correct.

Step-by-step solution

- Analyzing Statement (a)

Examine the claim about ozone: 'Ozone layer is harmful when present in troposphere and protects life when present in stratosphere.' Ozone in the troposphere acts as a pollutant and is harmful to living organisms, while in the stratosphere, it forms the ozone layer which protects life by blocking harmful UV radiation.

- Analyzing Statement (b)

Evaluate the statement: 'The industrial usage of fluorocarbons is very high because they can be manufactured cheaply.' Fluorocarbons are widely used in industry due to their stable and non-flammable nature, but their low cost of production is not the primary reason for their high usage. Therefore, this statement is not primarily correct.

- Analyzing Statement (c)

Evaluate the statement: 'Acid rains contain the oxoacids of sulphur and nitrogen.' Acid rain is primarily caused by the presence of sulfuric acid \((H_2SO_4\)) and nitric acid \((HNO_3\)), which are oxoacids of sulfur and nitrogen respectively.

- Drawing Conclusion

From the analysis, statement (a) about ozone is correct, and statement (c) about acid rain is also correct. However, statement (b) is not primarily accurate. Therefore, the correct answer is the option that includes only options (a) and (c).

Key concepts

Ozone Layer

The ozone layer is an integral part of Earth's atmosphere, playing a dual role depending on its location. When ozone is present in the stratosphere (the second layer of the atmosphere), it acts as a protective shield. This shield absorbs and blocks the majority of the sun's harmful ultraviolet (UV) radiation, which can cause skin cancer and cataracts in humans, and harm marine ecosystems.

However, when ozone is found in the troposphere (the lowest layer of the atmosphere), it becomes a pollutant. Tropospheric ozone is harmful as it can cause respiratory issues, aggravate asthma, and reduce lung function. It is also a significant greenhouse gas, contributing to global warming and climate change.

In summary:

• Stratospheric ozone: Protective, absorbs UV radiation.
• Tropospheric ozone: Harmful pollutant, respiratory irritant, greenhouse gas.

Acid Rain

Acid rain is a form of precipitation that contains high levels of hydrogen ions (low pH). It occurs when sulfur dioxide \((SO_2)\) and nitrogen oxides \((NO_x)\) are released into the atmosphere through activities like fossil fuel combustion and industrial processes. These gases react with water vapor and other chemicals to form acidic compounds like sulfuric acid \((H_2SO_4)\) and nitric acid \((HNO_3)\).

These acids fall to the ground in rain, snow, or fog, causing environmental damage. Acid rain can harm aquatic ecosystems by lowering the pH of water bodies, making them uninhabitable for some species. It also affects forests, deteriorating leaves and bark, and weakening trees.

Key points about acid rain:

• Caused by: Release of \(SO_2\) and \(NO_x\).
• Composed of: Sulfuric acid \((H_2SO_4)\) and nitric acid \((HNO_3)\).
• Effects: Harms aquatic ecosystems, damages forests, erodes buildings and monuments.

Fluorocarbons

Fluorocarbons are a group of chemical compounds derived from hydrocarbons, where some or all hydrogen atoms are replaced with fluorine atoms. They are known for their stability, non-flammability, and low toxicity. These properties make them highly valuable in various industrial applications, such as refrigerants, solvents, and in the production of Teflon.

One important aspect about fluorocarbons is their environmental impact. Many fluorocarbons are potent greenhouse gases and contribute to global warming. For example, chlorofluorocarbons (CFCs) were once widely used in refrigeration but were found to deplete the ozone layer. Their production has been largely phased out under international agreements like the Montreal Protocol.

Summary of fluorocarbons:

• Properties: Stable, non-flammable, low toxicity.
• Uses: Refrigerants, solvents, Teflon production.
• Environmental impact: Potent greenhouse gases, some deplete the ozone layer.