Environmental Chemistry

Photochemical smog, also known as Los Angeles-type smog, is a type of air pollution that forms when sunlight acts on certain pollutants.
The primary pollutants that lead to photochemical smog are nitrogen oxides (NOx) and volatile organic compounds (VOCs), which are emitted from vehicle exhausts and industrial processes.
The key chemical reactions involve sunlight (photo-) splitting nitrogen dioxide (NO ) to form nitric oxide (NO) and a highly reactive atomic oxygen (O).
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This atomic oxygen then reacts with molecular oxygen ( ) to form Ozone ( ), which is a major component of photochemical smog.
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The reactive atomic oxygen and ozone also react with the VOCs in the atmosphere to produce a variety of harmful secondary pollutants. These include:
- Formaldehyde (HCHO)
- Acrolein (CH =CHCHO)
- Peroxyacetyl nitrate (PAN)
These secondary pollutants cause eye irritation and respiratory problems.
Sulphur dioxide ( ), on the other hand, is the primary pollutant responsible for classical smog, also known as London-type or sulfurous smog. This type of smog forms in cool, humid conditions and is characterized by high concentrations of SO , sulfuric acid aerosols, and particulate matter from the burning of sulfur-rich fossil fuels like coal.
Therefore, sulphur dioxide is not a common component of photochemical smog.

Step 1: Analyze Statement-I (Components of Photochemical Smog).
Photochemical smog is formed from the reaction of sunlight with nitrogen oxides and volatile organic compounds (VOCs) in the atmosphere.
The carbon-containing components that are products of this process include:
- Acrolein ( ).
- Methanal (Formaldehyde, ).
- PAN (Peroxyacyl nitrates, e.g., ).
The statement listing acrolein, methanal, and PAN as carbon-containing components of photochemical smog is correct.

Step 2: Analyze Statement-II (Number of Greenhouse Gases).
Greenhouse gases (GHGs) are those gases in the Earth's atmosphere that absorb and emit radiation within the thermal infrared range, causing the greenhouse effect. They include compounds that contain at least two different atoms (diatomic molecules like are generally not GHGs).
The list is: .
- (Methane): A potent GHG. ( )
- (Carbon Dioxide): The most significant human-caused GHG. ( )
- (Nitric Oxide): Not a primary GHG in the context of global warming (its dimer and are, but is mostly involved in photochemical reactions). However, in many lists, is often considered a short-lived radiative-forcing agent. (Nitrous Oxide) is a major GHG. Assuming the question intended the major GHGs: is not typically counted as a major GHG. Let's assume it's not a GHG.
- (Liquid Water): Water vapor is a GHG, but liquid water is not a gas. ( )
- (Water Vapor): A major natural GHG. ( )
- (Oxygen): Not a GHG. ( )
- (Ozone): A GHG (both tropospheric and stratospheric). ( )
The greenhouse gases in the list are . This is a count of 4.
The statement claims the number is 5. Therefore, Statement-II is not correct.

Step 3: Conclude the final answer.
Statement I is correct, but Statement II is not correct.

Let's analyze the effects of the given gaseous pollutants.
(A) SO (Sulfur dioxide): SO is a major air pollutant, primarily from burning fossil fuels containing sulfur. It is an irritant to the respiratory system and can cause conditions like bronchitis and asthma, but NO is more strongly linked to acute disease in children.
(B) CO (Carbon dioxide): CO is a greenhouse gas and an asphyxiant at very high concentrations, but it is not typically considered a lung irritant or a cause of respiratory disease at normal pollutant levels.
(C) CO (Carbon monoxide): CO is a toxic gas that works by binding to hemoglobin and preventing oxygen transport in the blood (chemical asphyxiation). It does not primarily act as a lung irritant.
(D) NO (Nitrogen dioxide): NO is a reddish-brown gas, a major air pollutant from vehicle exhaust and industrial processes. It is a powerful lung irritant that can damage the respiratory tract. High-level exposure can cause inflammation of the lungs. It is particularly harmful to children and is known to increase their susceptibility to acute respiratory illnesses like bronchitis and pneumonia.
Given the options, NO is the most fitting description of a lung irritant that can lead to acute respiratory disease in children.

Step 1: Understanding the Concept:

Ozone depletion is driven by radical chain reactions in the stratosphere. We identify the substances that act as sources of these radicals or as catalysts for ozone destruction versus those that might act as sinks or have a lesser primary role.
Step 2: Analysis of Compounds:

(A) (Nitric Oxide): Acts as a catalyst in ozone depletion ( ). (B) (CFC-12): A major source of chlorine radicals ( ) which destroys ozone. (D) : Can photodissociate to yield chlorine radicals, directly contributing to depletion. (C) (Methane): While it is a greenhouse gas, its role in stratospheric chemistry is often to remove chlorine radicals by reacting with them to form HCl ( ). This effectively locks up the destructive chlorine in a reservoir species, temporarily mitigating depletion. Thus, it is not primarily responsible for the *depletion* mechanism itself compared to the others.
Step 3: Conclusion:

Methane is less responsible for depletion than NO, CFCs, and Chlorine gas.
Step 4: Final Answer:

is the correct answer.

Step 1: Understanding the Concept:
This question relates to environmental chemistry and the standard permissible limits of metal ions in drinking water as set by health organizations like the WHO or national bodies like the Bureau of Indian Standards (BIS).
Step 2: Analyzing Standard Data:
According to the Bureau of Indian Standards (BIS:10500) and WHO guidelines for drinking water quality: - The maximum permissible limit for Copper (Cu) is typically around 1.5 mg/L (or 1.5 mg dm⁻³). - The maximum permissible limit for Zinc (Zn) is typically around 15 mg/L (or 15 mg dm⁻³). Let's assume the variable `x` in the question refers to the maximum prescribed concentration of copper. So, mg dm⁻³. The maximum prescribed concentration of zinc is mg dm⁻³. Step 3: Evaluating the Options based on Standard Data:
The question asks for the concentration of zinc. The actual value is approximately 15 mg dm⁻³. The value of x is approximately 1.5 mg dm⁻³. Let's check the options: (A) . The required zinc concentration is 15. So this is incorrect. (B) . Incorrect. (C) . Incorrect. (D) . Incorrect. None of the options logically connect the standard limits of copper and zinc. The ratio of the permissible limits is Zn/Cu = 15/1.5 = 10. The options provided are nonsensical fractions. Therefore, the question is considered erroneous. No logical solution can be derived.
Step 4: Final Answer:
Based on standard water quality guidelines, none of the provided options are correct. The question is ill-posed or contains significant errors.