Environmental Chemistry MCQ Quiz - Objective Question with Answer for Environmental Chemistry - Download Free PDF

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

Concept:

In photochemical smog, nitrogen oxides, and hydrocarbons are primary pollutants whereas ozone and acrolein are secondary pollutants.

A chemical reaction between solar ultraviolet radiation and an atmosphere polluted with hydrocarbons and oxides of nitrogen causes photochemical smog. This is especially common from automobile exhaust. Smog can happen both during the day and at night, but photochemical smog only happens in the presence of sunlight.

Photochemical smog is composed of primary and secondary pollutants. Primary pollutants, which include nitrogen oxides and volatile organic compounds, are introduced into the atmosphere via vehicular emissions and industrial processes.

Photochemical smog is a type of smog produced when ultraviolet light from the sun reacts with nitrogen oxides in the atmosphere. It is visible as a brown haze, and is most prominent during the morning and afternoon, especially in densely populated, warm cities.

Correct answer: 1) 

Concept:

• Dinitrogen and dioxygen are the stable forms of nitrogen and oxygen atoms respectively.
• Dinitrogen has a very high bond enthalpy as it has triple bond.
• Due to this reason, it is practically inert at room temperature.
• However, the reactivity of dinitrogen increases as the temperature is increased.
• Dioxygen is a very reactive gas but due to presence of double bond the bond enthalpy of dioxygen is very high.

Explanation:

• Dinitrogen and dioxygen are main constituents of air (N2=78.08%,O2=20.95%" id="MathJax-Element-4-Frame" role="presentation" tabindex="0">N₂=78.08%,O₂=20.95%)
• They do not react with each other to form oxides of nitrogen.
• This is because dinitrogen has a triple bond between the two nitrogen atoms and for dinitrogen and dioxygen to react, this triple bond needs to be broken.
• But the bond dissociation energy that is the energy required to break the bond is very high for dinitrogen.
• This high amount of energy cannot be found in the atmosphere.
• Therefore, for this reaction to take place, it would require very high temperatures to generate enough energy to break the triple bond in dinitrogen.

Conclusion:

Thus, dinitrogen and dioxygen are main constituents of air but these do not react with each other to form oxides of nitrogen because the reaction is endothermic and requires very high temperature.

Additional Information

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.

Correct answer: 1)

Concept:

• Ozone is an important constituent of the stratosphere at altitudes between 15 and 25 km.
• It is formed in the atmosphere by the decomposition of oxygen by ultra-violet radiation from the sun having wavelength shorter than 260 nm. 
• Recently in 1980, scientists have observed a hole in the ozone blanket covering the upper atmosphere around Antarctica.
• Recent observations have also shown that the ozone layer diminishes over the south pole in spring during August-September to a greater extent year after year.
• This depletion of the protective blanket of ozone will cause a damaging effect because harmful ultra-violet rays can reach earth through this hole.
• The increased level of ultra-violet rays will result in damage to plants, animals, human beings and even matter posing great threat to ecosystem over the globe.

Explanation:

• The thick layer of ozone is called ozone blanket because it is very effective in absorbing harmful ultra violet rays given out by the sun.
• Therefore, the ozone layer is also known as protective shield.
• Ozone is also one of the greenhouse gas.
• The contribution of O₃  to the greenhouse effect is about 8 to 10%.
• About 75% of solar energy is absorbed by the surface of the earth, and the rest is radiated back to the atmosphere.
• This heat traps gases like CO₂, CH₄, O₃, CFC’s and H₂O  present in the atmosphere and adds to the heat of the atmosphere, causing global warming.

Conclusion:

Thus, the statement Ozone is not responsible for green house effect is wrong.
 

The correct answer is: "It has low concentration of oxidising agent."

Key Points

• Photochemical Smog Characteristics:
  • Photochemical smog, also known as "oxidizing smog," forms when sunlight reacts with pollutants like nitrogen oxides (NO_x) and volatile organic compounds (VOCs).
  • It contains a high concentration of oxidizing agents, such as ozone (O₃), peroxyacetyl nitrate (PAN), and other free radicals, which are harmful to both health and the environment.
  • This high concentration of oxidizing agents leads to respiratory problems, eye irritation, and damage to plants and materials.
• Control Measures for Photochemical Smog:
  • Reducing the release of precursors such as NO₂, hydrocarbons, and ozone is critical in controlling photochemical smog.
  • Improved vehicle emission standards, reduction in industrial emissions, and use of cleaner fuels are effective control measures.
  • Certain plants, such as pinus, neem, and tulsi, can help mitigate smog by absorbing pollutants and improving air quality.
• Incorrect Statement:
  • The statement "It has low concentration of oxidising agent" is incorrect because photochemical smog is characterized by a high concentration of oxidizing agents, which differentiates it from other types of smog, such as reducing smog (London smog).

Additional Information

• Formation of Photochemical Smog:
  • Occurs primarily in urban areas with high vehicular traffic and industrial activity under sunny conditions.
  • The reaction involves nitrogen oxides and hydrocarbons in the presence of sunlight, producing secondary pollutants like ozone and PAN.
• Impact of Photochemical Smog:
  • Adversely affects human health by causing respiratory problems, reduced lung function, and eye irritation.
  • Damages crops, reducing agricultural productivity, and negatively impacts plant health.
  • Causes the deterioration of materials like rubber, plastics, and metals due to the oxidative action of smog.
• Control Methods:
  • Encouraging public transportation and use of alternative fuels like CNG to reduce vehicular emissions.
  • Implementing stricter emission regulations for industries and vehicles.
  • Planting more vegetation in urban areas to naturally filter pollutants.

Concept:

Sun emits UV-radiations, which according to following EM categorisation have the wavelength range from 1 nm to 400 nm.

Concept:

Things float when they are positively buoyant or less dense than the fluid in which they are sitting.

Dichloromethane, DCM (CH₂Cl₂) is heavier (density = 1.3266g cm^-3)) than water (density = 1 g cm^-3).

So, DCM and H₂O will stay as lower and upper layer respectively in the separating funnel (S.F).

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.

Correct answer: 1 and 2)

Concept:

• Gases such as CO₂ , NO₂ , CFCs (chloro fluorocarbons) allow sun rays to pass through them but then absorb and reradiate the heat back towards the earth. These are therefore termed as green house gases.
• Radiations (ultra violet) from the sun penetrate the earth’s atmosphere and reach earth.
• The surface of earth partially absorbs the radiations.
• The rest is re-radiated as infrared radiation from the earth’s surface.
• In polluted air, molecules of CO₂, CH₄, CFCs, N₂O, O₃ and water vapours are present.
• These gases can absorb infrared radiations but cannot absorb the ultra violet radiations.
• Energy of these trapped radiations raise the temperature of earth and its atmosphere.
• Thus if proportion of green house gases increases in the atmosphere heat trapped by them will raise the temperature of the earth and will cause global warming.
• Greenhouse effect leading to global warming shall have severe effects on rainfall, sea level, plant and animal growth. 

Explanation:

• Global warming is the rate at which solar radiation are arriving the earth remain constant but the amount CO₂ in the air increaes.
• The heat radiated back to the earth will increase consequently.
• The temperature of the earth surface will increase.
• This increase in temperature will disturb the thermal balance on the earth and could car glaciers and ice caps to melt.
• About 75% of the solar energy reaching the earth is absorbed by the earth's surface, which increases the temperature.
• The rest of the heat radiates back to the atmosphere.
• The average global temperature will increase to a level which may lead to melting of polar ice caps and flooding of low lying area all over the earth.
• Increase in the global temperature increases the incidence of infectious diseases like dengue, malaria, yellow fever, sleeping sickness etc.

Conclusion:

Thus, the consequences of global warming may be increase in average temperature of the earth and melting of Himalayan Glaciers.

Additional Information

Correct answer: 2,3 and 4)

Concept:

• Acid rain, or acid deposition, is a broad term that includes any form of precipitation with acidic components, such as sulfuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms.  
• This can include rain, snow, fog, hail or even dust that is acidic. 
• Acid Rain or different sorts of precipitation that contain raised hydrogen particle levels, making it acidic, are alluded to as acid rain.
• Raised degrees of hydrogen particles cause the rain to have a low pH, making it harming amphibian animals and plants.
• Acid rain created when sulfur dioxide and nitrogen oxide outflows respond with environmental water atoms and produce acid.

Explanation:

• Acid rain containg H₂SO₄, HNO₃,H₂CO₃ (and small amount of HCl) which are formed from the oxide S and N₂ present in the air is called as acid rain.
• The pH of acid rain is in the range of 4-5.
•  The oxide of nitrogen undergo oxidation reaction.
• The reaction with the water vapour present in the atmosphere to form HNO₃. 
• The SO₃ reacts with water vapour and formed H₂SO₄ .
• The HNO₃ and H₂SO₄ combine with HCl present in the air to produce acidic precipitation which is called as acid rain.
• In acid rain H₂SO₄ = 60 - 70% ; HNO₃ = 30 - 40 % ; HCl = Very small amount.
• The normal rain water has a pH about 5.6 due to dissolution of CO₂ in water. 
• CO₂ react with water to form carbonic acid (H₂CO₃).
• When pH of rain water become less than 5.6 it will be acidic.

Conclusion:

Thus, the acids present in acid rain are H₂SO₄, HNO₃ and H₂CO₃. 

Additional Information