Environmental Chemistry MCQ Quiz in मराठी - Objective Question with Answer for Environmental Chemistry - मोफत PDF डाउनलोड करा

CONCEPT:

Photochemical Smog

• Photochemical smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes. These pollutants react in the atmosphere in the presence of sunlight to form secondary pollutants that contribute to the smog.
• It typically contains a mixture of pollutants including:
  • Nitrogen oxides (NO and NO₂)
  • Ozone (O₃)
  • Volatile organic compounds (VOCs) such as aldehydes (e.g., formaldehyde, HCHO)

EXPLANATION:

• The components of photochemical smog are primarily formed through the reaction of sunlight with pollutants like nitrogen oxides and VOCs. Specifically:
  • NO (Nitric oxide): Emitted directly from vehicles and industrial processes.
  • NO₂ (Nitrogen dioxide): Formed by the oxidation of NO in the atmosphere.
  • HCHO (Formaldehyde): A type of VOC formed from various hydrocarbon emissions.
• SO₂ (Sulfur dioxide) is generally not a component of photochemical smog, as it is more associated with industrial processes and the combustion of sulfur-containing fuels. While SO₂ can contribute to air pollution, it does not play a significant role in the formation of photochemical smog.

Therefore, the photochemical smog does not generally contain SO₂.

Correct answer: 2)

Concept:

• The ozone hole has developed because people have polluted the atmosphere with chemicals containing chlorine and bromine.
• The primary chemicals involved are chlorofluorocarbons (CFCs for short), halons, and carbon tetrachloride.

Explanation:

• Ozone layer depletion is caused due to CFCs.
• So, chlorine nitrate, which is found in the stratosphere causes the breakdown of the ozone layer.
• In Antarctica, several reactions take place in the stratospheric clouds, which cause the formation of chlorine nitrate which leads to ozone depletion.
• Chlorine is highly reactive and it interacts with ozone and hence destroys the ozone layer.

Conclusion:

Thus, ozone layer depletion in the Antarctica region is mainly due to the formation of chlorine nitrate.

Correct answer: 3) 

Concept:

• Smog is a mixture of smoke, dust particles and small drops of fog. It is a major air pollutant in big cities.
• Smog is of two types.
• Classical Smog:  This type of smog is formed by the combination of smoke, dust and fog containing sulphur dioxide from polluted air.
• This is also called chemical smog. Chemically, it is a reducing mixture so it is also called reducing smog. 
• Photochemcial Smog :This type of smog is formed by the combination of smoke, dust and fog with an air pollutant in the atmosphere as a result of photochemical reaction. 
• It can cause coughing, wheezing bronchial constriction and Peroxyaetyl nitrates and aldehydes found in smog are eye irritants.
• Materials are also adversely affected by some smog components.

Explanation:

• Photochemical smog occurs in warm, dry and sunny climate.
• The main components of the photochemical smog result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories.
• Photochemical smog has high concentration of oxidising agents and is, therefore, called as oxidising smog.
• This occurs in the months of summer when NO₂ and hydrocarbons are present in large amounts in the atmosphere.
• Concentration of O₃, PAN, aldehydes and ketones increases up in the atmosphere.
• SO₂ is not responsible for photochemical smog.
• NO₂  absorbs u.v. radiations and the entire cycle starts again.
• Both NO₂ and O₃ are strong oxidizing agents and can react with unburnt hydrocarbons (from exhaust of automobiles) to form organic free radicals.
• The formation of organic free radicals results into a number of chain reactions producing many undesirable compounds (such as formaldehyde, acrolein, organic peroxides, organic hydroperoxides, peroxyacyl nitrates etc.) which constitute photochemical smog. 

Conclusion:

Thus, SO₂ is not the components of photochemical smog.

Key Points

• The ozone layer in the stratosphere is affected by the increase in the atmospheric concentration of CFC(chlorofluorocarbons).
• In the atmosphere, CFCs drift slowly upward to the stratosphere, where they are broken up by ultraviolet radiation, releasing chlorine atoms, which can destroy ozone molecules.
• CFCs are the main reason for the Ozone hole.
• The other reasons for ozone depletion are a wide range of industrial and consumer applications, mainly refrigerators, air conditioners (hydrochlorofluorocarbons (HCFCs), and fire extinguishers.

Concept:

N₂ molecule has minimum role in the formation of photochemical smog. While CH₂ = O, O₃ and NO has major role. When fossil fuels are burnt, a variety of pollutions are emiited.

Two of them are hydrocarbons (unburnt) and NO. When these pollutants build upon high levels, a chain reaction occurs from their interaction with sunlight. The reactions involved in the formation of photochemical smog are as follows;

\({\rm{N}}{{\rm{O}}_2}\left( {\rm{g}} \right)\mathop \to \limits^{{\rm{hv}}} {\rm{NO}}\left( {\rm{g}} \right) + {\rm{O}}\left( {\rm{g}} \right)\)

O (g) + O₂ (g) ⇌ O₃ (g)

NO (g) + O₃ (g) → NO₂ (g) + O₂ (g)

O₃ (g) Reacts with unburnt hydrocarbons to produce chemicals such as formaldehyde, acrolein and PAN.

CONCEPT:

Acid Rain

• Acid rain is a type of precipitation with a pH lower than normal rainwater, which usually has a pH of around 5.6 due to dissolved carbon dioxide forming weak carbonic acid.
• Acid rain occurs when sulfur dioxide (SO₂) and nitrogen oxides (NO_x) are emitted into the atmosphere and combine with water vapor to form strong acids like sulfuric acid (H₂SO₄) and nitric acid (HNO₃).
• The pH of acid rain is typically below 5.6, indicating its acidic nature.

EXPLANATION:

• The pH scale ranges from 0 to 14, where 7 is neutral, values below 7 indicate acidity, and values above 7 indicate basicity.
• Normal rainwater has a slightly acidic pH of 5.6 due to the presence of dissolved carbon dioxide (CO₂) forming carbonic acid.
• Acid rain has a pH lower than 5.6 because it contains stronger acids like sulfuric acid and nitric acid due to atmospheric pollution from industrial emissions, vehicle exhausts, and other sources.
• Among the given options:
  • Option 1 (Between 8-9) is incorrect, as this pH range is basic and not acidic.
  • Option 2 (Below 4.5) and Option 3 (Below 3.5) are overly low and typically not the average pH of acid rain.
  • Option 4 (Below 5.6) is correct, as this aligns with the definition of acid rain.

Therefore, the correct answer is Option 4: Acid rain has a pH below 5.6.

CONCEPT:

Greenhouse Gases

• Greenhouse gases are atmospheric gases that trap heat and contribute to the greenhouse effect, which warms the Earth's surface.
• Common greenhouse gases include:
  • Carbon dioxide (CO₂)
  • Methane (CH₄)
  • Water vapor (H₂O)
  • Nitrous oxide (N₂O)
• These gases absorb and emit infrared radiation, which contributes to global warming.

EXPLANATION:

• In the given options:
  • Option 1: CH₄ (Methane) is a greenhouse gas.
  • Option 2: CO₂ (Carbon dioxide) is a greenhouse gas.
  • Option 3: Helium (He) is NOT a greenhouse gas because it does not absorb infrared radiation. Helium is an inert noble gas and does not contribute to the greenhouse effect.
  • Option 4: Methane derivatives can also act as greenhouse gases depending on their chemical structure.

Therefore, Helium (Option 3) is the correct answer as it does not exhibit properties of a greenhouse gas.

CONCEPT:

Methods of Soil Protection

• Soil protection involves practices aimed at preventing soil degradation, erosion, and loss of fertility.
• Common methods of soil protection include afforestation, neutralizing acid rain, and minimizing the use of fossil fuels.

EXPLANATION:

• Among the given options:
  • Afforestation: Planting trees helps prevent soil erosion by binding soil particles with roots. It is a widely used soil protection method.
  • Neutralization of acid in rain by adding lime: Adding lime to soil can counteract the acidity caused by acid rain, helping to maintain soil health.
  • Uses of excess fertilizers: Excessive use of fertilizers harms soil health by causing nutrient imbalance and pollution. This is not a method of soil protection; rather, it contributes to soil degradation.
  • Minimizing use of fossil fuels: Reducing fossil fuel use helps decrease air pollution and acid rain, indirectly protecting soil from acidification.

Option 3, "Uses of excess fertilizers," is not a method of soil protection.

CONCEPT:

Polluting Strength of Water

• The polluting strength of water is a measure of the level of pollution in water due to organic matter. It is commonly assessed using biochemical parameters.
• Biochemical Oxygen Demand (BOD) is the most widely used parameter to gauge the polluting strength of water.
• BOD represents the amount of dissolved oxygen required by microorganisms to break down organic matter in water under aerobic conditions.

EXPLANATION:

• Biochemical Oxygen Demand (BOD) is directly related to the presence of organic pollutants in water. Higher BOD values indicate higher levels of organic pollution.
• Although other parameters like Chemical Oxygen Demand (COD) also measure pollution, COD includes both biodegradable and non-biodegradable organic pollutants. BOD specifically focuses on biodegradable pollutants, making it more relevant for assessing polluting strength.
• Other parameters listed, such as saline content or amounts of phosphates and carbonates, do not specifically indicate the polluting strength due to organic matter.
• Therefore, BOD is the correct answer as it directly reflects the polluting strength of water.

Thus, the correct answer is BOD in water.

CONCEPT:

Environmental Chemistry – Common Misconceptions & Facts

• Ammonium salts contribute to atmospheric haze by forming secondary aerosols through chemical reactions in the atmosphere.
• Chlorine radicals (Cl˙) do not produce ozone but rather destroy it. They react with ozone (O₃) and decompose it into molecular oxygen (O₂):

  Cl˙ + O₃ → ClO˙ + O₂

• Polychlorinated biphenyls (PCBs) are toxic organic compounds used as dielectric fluids in transformers and coolants—not cleansing solvents. They are persistent environmental pollutants.
• ‘Blue baby’ syndrome (methemoglobinemia) is caused by the presence of excess nitrate (NO₃⁻) ions in drinking water, not sulphate ions.

EXPLANATION:

• Statement A: Correct – Ammonium salts contribute to atmospheric haze.
• Statement B: Incorrect – Chlorine radicals deplete ozone, not produce it.
• Statement C: Incorrect – PCBs are toxic pollutants, not cleansing agents.
• Statement D: Incorrect – Blue baby syndrome is linked to nitrates, not sulphates.

Therefore, the correct answer is A and C only