All questions of Environmental Chemistry for NEET Exam

A greenhouse is a house made of glass. It has glass walls and a glass roof. People grow tomatoes and flowers and other plants in them. A greenhouse stays warm inside, even during winter. Sunlight shines in and warms the plants and air inside. But the heat is trapped by the glass and can't escape. So during the daylight hours, it gets warmer and warmer inside a greenhouse, and stays pretty warm at night too.

A physical, biological or chemical alteration to the air in the atmosphere can be termed as pollution. It occurs when any harmful gases, dust, smoke enters into the atmosphere and makes it difficult for plants, animals and humans to survive as the air becomes dirty.

Tropospheric pollution occurs due to the presence of undesirable solid or gaseous particles in the air.

The layer above the troposphere is called the stratosphere. Nearly all of the water vapor and dust particles in the atmosphere are in the troposphere. That is why most clouds are found in this lowest layer, too. The bottom of the troposphere, right next to the surface of Earth, is called the "boundary layer".

The main chemicals in air pollution that create acid rain are sulfur dioxide (SO2) and nitrogen (NOx). Acid rain usually forms high in the clouds where sulfur dioxide and nitrogen oxides react with water, oxygen, and oxidants. this mixture forms a mild solution of sulfuric acid and nitric acid.

Explanation:
BOD stands for Biological Oxygen Demand, which is the amount of dissolved oxygen required by microorganisms to decompose the organic matter present in water. The higher the BOD, the more organic matter is present, and the more polluted the water is.

Clean water has a lower BOD compared to highly polluted water because it contains less organic matter. Therefore, the correct answer is option B, which states that:

- Clean water has a BOD of 5ppm
- Highly polluted water has a BOD of 17ppm

It is important to note that different bodies of water have different BOD levels, and some may even have BOD levels below 5ppm. However, a BOD level of 17ppm is considered highly polluted and can have negative impacts on aquatic life and human health.

Man-made causes of depletion of ozone layer: The main cause for the depletion of ozone is determined as excessive release of chlorine and bromine from man-made compounds such as chlorofluorocarbons (CFCs).

Currently, oil burning is responsible for about 30% of all carbon dioxide emissions to air. Natural gas does not release as much carbon,cooper dioxide because of its methane structure. The largest emissions are cause by coal combustion. Coal may result in underground fires that are virtually impossible to extinguish

Eutrophication
Eutrophication is the process in which nutrient-enriched water bodies support a dense plant population, leading to the death of animal life due to oxygen deprivation and subsequent loss of biodiversity. It is an environmental issue that can have significant ecological and economic impacts.

Causes of Eutrophication
There are several factors that contribute to eutrophication:
1. Excessive Nutrient Inputs: The primary cause of eutrophication is the excessive input of nutrients, particularly nitrogen and phosphorus, into water bodies. These nutrients can come from various sources such as agricultural runoff, sewage discharge, and industrial activities.
2. Fertilizer Use: The use of fertilizers in agriculture can lead to nutrient runoff into nearby water bodies. When rain or irrigation water carries these nutrients into rivers, lakes, or oceans, it can result in eutrophication.
3. Sewage and Wastewater Discharge: Untreated or poorly treated sewage and wastewater discharge can introduce high levels of nutrients into water bodies, promoting the growth of algae and other aquatic plants.
4. Deforestation and Urbanization: Land-use practices such as deforestation and urbanization can increase the amount of sediment and nutrients entering water bodies. This sediment can contribute to the buildup of organic matter, further promoting eutrophication.

Process of Eutrophication
The process of eutrophication typically involves the following steps:
1. Nutrient Enrichment: Excessive nutrients, mainly nitrogen and phosphorus, enter the water body through various sources.
2. Algal Bloom: These nutrients stimulate the rapid growth of algae and other aquatic plants, leading to the formation of dense algal blooms. These blooms can turn the water green or brown and reduce water clarity.
3. Reduced Oxygen Levels: As the algae die and decompose, bacteria break down the organic matter, consuming oxygen in the process. This causes a decrease in the dissolved oxygen levels in the water.
4. Oxygen Depletion: The high oxygen demand from the decomposition of organic matter can deplete the available oxygen in the water, leading to hypoxic or anoxic conditions. This lack of oxygen can be detrimental to fish and other aquatic organisms, often resulting in their death.
5. Loss of Biodiversity: The depletion of oxygen and subsequent death of animal life can result in a loss of biodiversity in the affected water body. Fish, shellfish, and other organisms that rely on oxygen-rich water may not be able to survive in such conditions, leading to a decline in their populations.

Impacts of Eutrophication
Eutrophication can have several negative impacts on aquatic ecosystems:
1. Fish Kills: The oxygen depletion caused by eutrophication can lead to fish kills, especially in shallow water bodies where oxygen levels can drop rapidly.
2. Harmful Algal Blooms: Some algal blooms can produce toxins that are harmful to humans and marine life. These harmful algal blooms (HABs) can contaminate drinking water supplies and cause health issues in animals and humans.
3. Loss of Biodiversity: Eutrophication can result in the loss of biodiversity as fish and other aquatic organisms die off due to oxygen deprivation. This can disrupt the food chain and have cascading effects on the entire ecosystem.
4. Economic Losses: Eutrophication can have economic consequences, particularly for industries dependent on

Explanation:
Ozone in the stratosphere is formed by the action of UV radiation on dioxygen molecules. The process of ozone formation can be explained as follows:

1. Absorption of UV radiation: The ozone layer in the stratosphere absorbs high-energy UV radiation from the sun.

2. Dissociation of dioxygen molecules: The UV radiation dissociates (breaks apart) dioxygen molecules (O2) into two oxygen atoms (O).

3. Formation of ozone: The oxygen atoms then combine with other dioxygen molecules to form ozone (O3).

O2 + UV radiation → 2O
O + O2 → O3

4. Destruction of ozone: The ozone molecules can also be destroyed by UV radiation, which breaks them apart into oxygen molecules and oxygen atoms.

O3 + UV radiation → O2 + O

Therefore, the concentration of ozone in the stratosphere is determined by a balance between its formation and destruction.

Conclusion:
In conclusion, ozone in the stratosphere is formed by the action of UV radiation on dioxygen molecules, not on CFCs or chlorine atoms. The formation of ozone is an important process that helps to protect the earth from harmful UV radiation. However, human-made chemicals such as CFCs can destroy the ozone layer in the stratosphere, leading to an increase in UV radiation reaching the earth's surface.

Introduction
Unleaded paint and petrol were introduced as a replacement for leaded products due to the harmful effects of lead on human health and the environment.

Impact of Lead on Brain
Lead is a toxic metal that can have devastating effects on the human body, especially the brain. Research has shown that exposure to lead can cause mental impairment, including decreased IQ, poor attention span, and behavior problems.

Leaded Paint
Leaded paint was commonly used in the past as a pigment for coloring paint. However, as the harmful effects of lead on human health became apparent, leaded paint was phased out in many countries, including the US and Europe. Unleaded paint, which uses alternative pigments, is now widely used in the painting industry.

Leaded Petrol
Leaded petrol was introduced in the early 20th century as a way to improve engine performance. However, it was later discovered that leaded petrol releases toxic lead particles into the air when burned, leading to serious health problems. Unleaded petrol was introduced as a replacement, which is now widely used in many countries.

Conclusion
Unleaded paint and petrol were introduced primarily to reduce the harmful effects of lead on human health and the environment. The use of these alternative products has significantly improved public health and reduced environmental pollution.

Photochemical smog occurs in warm, dry and sunny climate. It is formed by the action of sunlight on unsaturated hydrocarbons and nitrogen oxides. Chemically, it is an oxidising mixture. It does not involve any smoke or fog.

In summer season, nitrogen dioxide and methane react with chlorine monoxide and chlorine free radicals forming chlorine sinks, preventing much ozone depletion, whereas in winters, special type of clouds, called the polar stratospheric clouds are formed over Antarctica.These polar stratospheric clouds provide surface on which chlorine nitrate gets hydrolysed to form hypochlorous acid. It also reacts with hydrogen chloride to give molecular chlorine.

The correct answer is option 'D' - Ozone layer. Let's delve into the details to understand why.

The Stratosphere:
The stratosphere is a layer of the Earth's atmosphere that lies above the troposphere and below the mesosphere. It is situated roughly between 10 and 50 kilometers (6-30 miles) above the Earth's surface. The stratosphere plays a crucial role in protecting life on Earth by containing the ozone layer, which absorbs harmful ultraviolet (UV) radiation from the sun.

The Ozone Layer:
The ozone layer is a region within the stratosphere that contains a higher concentration of ozone (O3) molecules. Ozone is a molecule made up of three oxygen atoms bonded together. This layer is located between approximately 10 and 50 kilometers (6-30 miles) above the Earth's surface.

Importance of the Ozone Layer:
The ozone layer is vital because it acts as a shield, absorbing most of the sun's harmful UV radiation. UV radiation can cause various health issues, including skin cancer, cataracts, and weakened immune systems. It can also harm ecosystems, including marine life, crops, and phytoplankton.

Formation and Stability of the Ozone Layer:
The ozone layer is formed and maintained by a balance of chemical reactions involving oxygen molecules (O2) and ozone (O3). Solar UV radiation breaks apart some oxygen molecules into individual oxygen atoms. These free oxygen atoms then react with other oxygen molecules to form ozone. The ozone molecules, in turn, absorb UV radiation and prevent it from reaching the Earth's surface.

Depletion of the Ozone Layer:
Human activities have led to the release of certain chemicals, called ozone-depleting substances (ODS), into the atmosphere. The most well-known ODS are chlorofluorocarbons (CFCs) and halons, which were commonly used in refrigerants, aerosol propellants, and fire extinguishing systems. ODS can reach the stratosphere and disrupt the balance of ozone formation and destruction, leading to ozone depletion.

Consequences of Ozone Depletion:
Ozone depletion allows more UV radiation to reach the Earth's surface, which can have adverse effects. Increased UV radiation can cause skin cancer, damage to the eyes, suppression of the immune system, and harm to marine ecosystems, agriculture, and the overall environment. To mitigate ozone depletion, the international community developed the Montreal Protocol in 1987, which regulates the production and consumption of ozone-depleting substances.

In conclusion, the stratosphere is a region of the atmosphere that contains the ozone layer. The ozone layer is crucial for protecting life on Earth by absorbing harmful UV radiation from the sun. Ozone depletion caused by human activities can have severe consequences, highlighting the importance of preserving and safeguarding the ozone layer.