Problem 17 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Taj Mahal is being slowly disfigured and discoloured. This is primarily due to : (a) Global warming (b) Acid rain (c) Water pollution (d) Soil pollution

Step-by-Step Solution

Answer

The primary cause is (b) Acid rain.

Step 1: Understand the problem

The exercise asks for the primary cause of the disfigurement and discoloration of the Taj Mahal. We need to identify factors that would lead to such issues in historical buildings.

Step 2: Analyze Each Option

- **Global warming:** Typically contributes to climate change but not directly to discoloration of specific buildings. - **Acid rain:** Formed by sulfur dioxide and nitrogen oxides in the air reacting with water, leading to acidification. It is known to damage and discolor stone, particularly marble, which is what the Taj Mahal is made of. - **Water pollution:** Refers to contamination in rivers, lakes, and oceans. It's not typically associated with direct discoloration of buildings. - **Soil pollution:** Involves contaminants in the soil. It may affect plant growth but is unlikely to directly discolor or disfigure a marble structure like the Taj Mahal.

Step 3: Choose the Best Answer

Given the analysis, acid rain is the most likely culprit behind the discoloration of the Taj Mahal. The sulfur and nitrogen compounds contributing to acid rain are known to corrode marble.

Key Concepts

Sulfur Dioxide

Sulfur dioxide ( ext{SO}_{2}) is a colorless gas with a sharp odor, commonly released from burning fossil fuels such as coal and oil, and from volcanic eruptions. It plays a significant role in the formation of acid rain. When sulfur dioxide is emitted into the atmosphere, it reacts with water vapor to form sulfuric acid ( ext{H}_{2} ext{SO}_{4}). This transformation is essential in the context of acid rain, as sulfuric acid contributes to the acidification of rainwater.

Key points about sulfur dioxide include:

• It reacts with atmospheric components to create sulfuric acid.
• Contributes significantly to the environmental problem known as acid rain.
• Can lead to respiratory problems in humans and animals when present in high levels.

Understanding the role of sulfur dioxide in acid rain is critical because it directly impacts both human health and the integrity of buildings and monuments. For example, historical structures like the Taj Mahal suffer from surface corrosion, discoloration, and structural fragility due to sulfuric acid exposure.

Nitrogen Oxides

Nitrogen oxides ( ext{NO}_{x}), such as nitric oxide ( ext{NO}) and nitrogen dioxide ( ext{NO}_{2}), are another group of gases involved in the formation of acid rain. These gases are primarily produced from engines of vehicles, power plants, and industrial processes. When nitrogen oxides are released into the atmosphere, they react with water to form nitric acid ( ext{HNO}_{3}).

Essential facts about nitrogen oxides include:

• Roles in forming acid rain alongside sulfur dioxide.
• Produced from many industrial activities and combustion engines.
• Contribute to environmental phenomena like smog and acidification of ecosystems.

The impact of nitrogen oxides on acid rain furthers ecological damage and directly affects the degradation of marble structures. This is evident in landmarks like the Taj Mahal, where nitric acid eats away at the marble, causing corrosion and discoloration over time. Tackling emissions of nitrogen oxides is crucial to reducing acid rain and protecting cultural heritage sites.

Marble Corrosion

Marble, a metamorphic rock primarily composed of calcium carbonate ( ext{CaCO}_{3}), is susceptible to corrosion from acid rain. When acidic rainwater, laden with sulfuric and nitric acids, comes into contact with marble, a chemical reaction occurs. This interaction leads to the dissolution of calcium carbonate to form soluble calcium compounds, resulting in surface erosion and loss of the stone's natural sheen.

Factors contributing to marble corrosion include:

• Exposure to sulfuric and nitric acid from acid rain.
• Deterioration of stone's aesthetic and structural qualities.
• Accelerated damage in polluted urban environments.

The venerable Taj Mahal is a prime example of an architectural treasure vulnerable to marble corrosion. Consistent exposure to acid rain causes significant visual and structural damage, highlighting the importance of strategies to control emissions of sulfur dioxide and nitrogen oxides. Protecting marble buildings requires coordinated efforts to mitigate airborne pollutants that drive acidification processes.