Environmental Chemistry

Statement I is correct, but statement II is not correct. The correct form of statement II is,

The number of greenhouse gases are three.

They are $\mathrm{CH}_4, \mathrm{CO}_2$ and $\mathrm{H}_2 \mathrm{O}(\mathrm{g})$.

Photochemical smog is formed by the reaction of sunlight with pollutants like nitrogen oxides ( $\mathrm{NO}_x$ ) and hydrocarbons (VOCs). Among the given compounds, only sulphur dioxide ( $\mathrm{SO}_2$ ) is not a typical component of photochemical smog. Instead, it is mainly associated with classical smog.

Nitrogen dioxide $\left(\mathrm{NO}_2\right)$ is a known air pollutant that acts as a strong lung irritant. When inhaled, it reacts with the moisture in the respiratory tract to form acids ( $\mathrm{HNO}_2$ ) and $\mathrm{HNO}_3$ ) that can damage the delicate lung tissue. Exposure to $\mathrm{NO}_2$ is particularly harmful to children, as it can increase their susceptibility to respiratory infections and lead to acute respiratory illnesses.

Let's examine the other options.

• Sulphure dioxide $\left(\mathrm{SO}_2\right)$ is also a potent lung irritant and a major cause of respiratory problems, especially in asthamtics. However, between the given options, $\mathrm{NO}_2$ is often specifically cited for its role in causing acute respiratory disease.

• Carbon dioxide $\left(\mathrm{CO}_2\right)$ is a simple asphyxiant at high concentrations,

meaning it displaces oxygen. It is not a long irritant.

• Carbon monoxide (CO) is a toxic gas that impairs the blood's ability to carry oxygen by binding to hemoglobin. It is not a lung irritant, Therefore, nitrogen dioxide $\left(\mathrm{NO}_2\right)$ is the correct answer.

The maximum prescribed concentration of zinc in drinking water is $15 \mathrm{mg} \mathrm{dm}^{-3}$. The maximum prescribed concentrations of copper is $1 \mathrm{mg} \mathrm{dm}^{-3}$ Thus, the correct option is $\frac{15}{x}$.

The correct statements are given in I and III. While II and IV are incorrect. Their correct forms are,

II. $\mathrm{NO}_2$ is not present in classical smog. It consist of $\mathrm{SO}_2$, fog, smoke.

IV. pH of rain water is around 5.6 .

🌍 Background:

The depletion of the ozone layer is mainly caused by halogen (Cl, Br) and nitrogen oxides (NOₓ) that catalytically destroy ozone (O₃) molecules in the stratosphere.

The main culprits are:

• CFCs (chlorofluorocarbons) such as CF₂Cl₂ (Freon-12).

• NO and NO₂ (from supersonic aircrafts, etc.) to a limited extent.

🔹 Option A: NO

• Nitric oxide (NO) can indeed react with ozone and participate in catalytic cycles that destroy ozone.

• So NO does contribute to ozone layer depletion.

✅ Primarily responsible.

🔹 Option B: CF₂Cl₂ (CFC-12)

• A chlorofluorocarbon that releases chlorine radicals (Cl·) under UV light in the stratosphere.

• These radicals catalytically destroy ozone.

• CFCs are the principal cause of ozone layer depletion.

✅ Primarily responsible.

🔹 Option C: CH₄ (Methane)

• Methane does not destroy ozone directly.

• In fact, methane can react with Cl· radicals, forming HCl and thereby reducing the concentration of ozone-depleting radicals to some extent.

• It is not a major ozone-depleting substance.

🚫 Not primarily responsible.

🔹 Option D: Cl₂ (Chlorine gas)

• Though molecular chlorine can destroy ozone, it doesn’t reach the stratosphere in large amounts due to high reactivity and solubility.

• However, under certain conditions, Cl₂ produced from CFC photolysis can release Cl atoms – so it is indirectly involved.

✅ Can contribute, though not directly emitted into stratosphere.

✅ Final Answer:

$ \boxed{\text{CH}_4} $

Methane (CH₄) is not primarily responsible for depletion of the ozone layer in the stratosphere.

$\mathrm{CO}_2$ (carbon dioxide) is a major contributor of global warming. $\mathrm{CO}_2$ molecules absorb infrared radiation emitted by earth's surface and re-radiate it, trapping some of heat within atmosphere.

Among the given options, statement (b) is incorrect regarding photochemical smog.

It is a mixture of $\mathrm{SO}_2$, nitrogen oxide and volatile organic compounds.

Statement (b) is incorrect regarding classicial smog. The correct form is classical smog is composed of $\mathrm{SO}_2$, smoke and fog.

Photochemical smog:

• Formed when sunlight acts on nitrogen oxides (NOx) and hydrocarbons (unburnt fuel), producing secondary pollutants like ozone (O₃), peroxyacetyl nitrate (PAN), formaldehyde, etc.

• It is also called Los Angeles smog or summer smog.

• It mainly occurs in warm, dry, and sunny climates.

Option A:

It is controlled by the use of catalytic converters in automobiles.

✅ Correct. Catalytic converters reduce emissions of NOx and hydrocarbons, which are precursors of photochemical smog.

Option B:

It causes corrosion of metals.

✅ Correct. Ozone and other oxidants in photochemical smog can corrode metals.

Option C:

It is a mixture of $ \mathrm{SO_2} $, smoke, and fog.

❌ Not correct.

This describes classical smog (also called London smog or reducing smog), which occurs in cool, humid conditions and is a mixture of SO₂ and particulates with fog.

Photochemical smog, on the other hand, contains NOx, hydrocarbons, and oxidants such as ozone—not SO₂-based smoke and fog.

Option D:

It causes extensive damage to plant life.

✅ Correct. Ozone and PAN damage leaves and affect photosynthesis.

✅ Final Answer: Option C — It is a mixture of SO₂, smoke and fog (Not correct for photochemical smog).

Nitrate $\left(\mathrm{NO}_3^{-}\right)$when present in excess in drinking water causes the disease methemoglobinemia.

(A) Pb > 50 ppm

→ Lead toxicity causes liver and kidney damage, neurological disorders, etc.

✅ So, (A) → (IV) Liver damage

(B) SO₄²⁻ > 500 ppm

→ High sulfate content in water has a laxative effect.

✅ So, (B) → (III) Laxative effect

(C) NO₃⁻ > 50 ppm

→ High nitrate levels cause methemoglobinemia (‘Blue baby’ syndrome) in infants.

✅ So, (C) → (II) ‘Blue baby’ syndrome

(D) F⁻ > 2 ppm

→ Excess fluoride causes fluorosis → brown mottling of teeth.

✅ So, (D) → (I) Brown mottling of teeth

✅ Correct matching:

A–IV, B–III, C–II, D–I

✅ Correct Answer: Option A

Among the gives options only methane is not responsible for depletion of ozone layer.

To match the metals with their maximum prescribed concentration in drinking water (in ppm), we can use the standard guidelines typically set by organizations like the World Health Organization (WHO). Based on common standards:

• Manganese (Mn) is typically limited to around 0.05 ppm.

• Zinc (Zn) typically has a higher tolerance and is often limited to around 3.0 ppm.

• Cadmium (Cd) is very toxic, so it is usually limited to around 0.005 ppm.

• Copper (Cu) is often limited to around 1.0 to 2.0 ppm, but for the sake of choosing from the given options, we will consider it the highest option which is 5.0 ppm here.

Now, let's match these with the given options:

• (A) Mn --> (I) 0.05

• (B) Zn --> (II) 3.0

• (C) Cd --> (III) 0.005

• (D) Cu --> (IV) 5.0

So, the correct matching is Option D:

A-I, B-II, C-III, D-IV

Due to presence of sulphur dioxide ( $\mathrm{SO}_2$ ) in high concentration in air, the flower buds get stiffed.

A is correct but R is not correct. The correct form of R is, haemoglobin has much higher affinity for CO , causing it to bind more strongly and displace oxygen. This stronger bond make carboxyhaemoglobin more stable than oxyhaemoglobin.

Eutrophication can lead to decrease in dissolved oxygen. Eutrophication is a phenomenon in which a water body become overly enriched with nutrients, leading to the plentiful growth of simple plant life. Excessive growth of algae and plankton is indicator of this process.

Thermal power plants generates non-biodegradable waste such as fly ash.

Non-biodegradable waste is defined as a substance that cannot be decomposed naturally.

The complete reaction is as follows.

Hence, compound $ X $ is $ \mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CHO} $.

Methemoglobinemia is a rare blood disorder that effects how red blood cells deliver oxygen throughout the body.

One of the main reason behind is excess of nitrate concentration in drinking water.

Photochemical smog primarily consists of secondary pollutants that form when sunlight reacts with pollutants such as nitrogen oxides and volatile organic compounds (VOCs). The common components of photochemical smog include ozone ($\mathrm{O}_3$), nitrogen oxides such as nitric oxide ($\mathrm{NO}$), and peroxyacetyl nitrate (PAN).

Therefore, the correct combination is:

Option D

$\mathrm{O}_3$ (ozone)

$\mathrm{NO}$ (nitric oxide)

$\mathrm{PAN}$ (peroxyacetyl nitrate)

Nitrogen oxides such as $\mathrm{NO}_2$, $\mathrm{N}_2 \mathrm{O}_2, \mathrm{~N}_2 \mathrm{O}_3$ and $\mathrm{N}_2 \mathrm{O}_5$ are irritating to the upper respiratory tract and lungs even at low concentration.

Lead is a heavy metal, and its permissible limit in drinking water is very low—typically measured in parts per billion (ppb). In the table, the 50 ppb value (List II, III) fits this criterion.

Sulphate is usually tolerated in higher concentrations in drinking water, and a limit like 500 ppm (List II, I) is acceptable.

Nitrate should be limited to around 50 ppm (List II, II) to ensure safety in drinking water.

Matching these:

Lead (A) → 50 ppb → III

Sulphate (B) → 500 ppm → I

Nitrate (C) → 50 ppm → II

This corresponds to Option C: A-III, B-I, C-II.

Chemical Oxygen Demand (COD) is a test used to determine the amount of oxygen needed to chemically oxidize the organic material present in water. This is measured by titrating the polluted water with a potassium dichromate solution in an acidic medium.

BOD or biochemical oxygen demand is the amount of dissolved exygen neeeded by aerobic biological organism to breakdown organic material present in water.

BOD for pure water < 5 ppm BOD for highly polluted water $\geq 17 \mathrm{ppl}$

In an automobile’s catalytic converter, certain platinum‐group metals are employed to transform toxic exhaust gases into less harmful ones. In general:

• Platinum (Pt) and Palladium (Pd) catalyze oxidation reactions such as

  $2CO + O_2 \longrightarrow 2CO_2$

which converts poisonous carbon monoxide (CO) into relatively harmless carbon dioxide (CO₂).

• Rhodium (Rh) catalyzes the reduction of nitrogen oxides. For example, it helps convert nitric oxide (NO) — which, along with its oxidized form nitric dioxide (NO₂), is a pollutant causing smog and respiratory problems — into nitrogen gas:

  $2NO \longrightarrow N_2 + O_2$

Now, the question states that the catalyst “prevents the release of gas Y into the atmosphere.” This implies that a toxic gas (one of the nitrogen oxides) is being converted into something benign instead. Of the options given, only one gas is a nitrogen oxide: NO₂.

Although in many converters the role of reducing NO (or NO₂) is mainly played by rhodium, among the answer choices the only pairing that involves a nitrogen oxide as “gas Y” is with palladium:

  Option A: $X = \mathrm{Pd},\quad Y = \mathrm{NO_2}.$

Thus, even though in practice a combination of Pt, Pd, and Rh is used, the option that correctly identifies a catalyst used in these converters (Pd being one of the platinum‐group metals used) along with the toxic nitrogen oxide (NO₂) that is converted (and so “prevented” from being released) is Option A.

Therefore, the answer is:

  X = Pd and Y = NO₂.

Answer: Option A.

Let's analyze the relationships step by step:

For fluoride in drinking water:

When the concentration is $<1\text{ ppm}$, there isn't enough fluoride to help strengthen teeth, which increases the risk of $\textbf{tooth decay}$.

A concentration of $>2\text{ ppm}$ typically leads to dental fluorosis, which manifests as $\textbf{brown mottling of teeth}$.

At very high levels, $>10\text{ ppm}$, the excessive fluoride can lead to skeletal fluorosis, which is harmful to the bones.

Matching the lists:

A: $<1\text{ ppm}$ ⟶ Tooth decay (Effect II)

B: $>2\text{ ppm}$ ⟶ Brown mottling of teeth (Effect III)

C: $>10\text{ ppm}$ ⟶ Harmful to bones (Effect I)

Thus, the correct matching is:

A-II, B-III, C-I

Therefore, the correct answer is:

Option D

A-II, B-III, C-I

The correct order of pesticide entered the market is organochlorides ar first, then organophosphate and in last sodium chlorate pesticides.

Freons are a class of compounds which are also known as chlorofluorocarbons (CFCs). As the name suggests, these compounds contain carbon, chlorine, and fluorine atoms. So the compound that is an example of a Freon from the options given is :

Option D : $\mathrm{C}_{2} \mathrm{Cl}_{2} \mathrm{F}_{2}$

This compound contains both chlorine and fluorine atoms bonded to carbon, and is therefore a CFC or a Freon.

Statement I : If BOD is 4 ppm and dissolved oxygen is 8 ppm, then it is a good quality water.

Statement II : If the concentration of zinc and nitrate salts are 5 ppm each, then it can be a good quality water.

The Biochemical Oxygen Demand (BOD) measures the quantity of oxygen used by microorganisms in the oxidation of organic matter. Lower values of BOD indicate better water quality. A BOD value of less than 5 ppm indicates good quality water. Therefore, in Statement I, the BOD value of 4 ppm indicates good water quality.

Dissolved oxygen (DO) refers to the level of free, non-compound oxygen present in water. DO levels above 5-6 ppm are generally good for aquatic life. In Statement I, the DO level of 8 ppm suggests the water is of good quality.

The concentration of zinc in clean water should not exceed 5 ppm and the concentration of nitrates should not exceed 50 ppm. In Statement II, both zinc and nitrate concentrations are given as 5 ppm, which are within their respective permissible limits, therefore suggesting the water can be of good quality.

Hence, based on this analysis :

Option C : Both the statements I and II are correct.

The delicate balance of $\mathrm{CO}_2$ and $\mathrm{O}_2$ is disturbed by the burning of coal (Option A), the burning of petroleum (Option B), and deforestation (Option D). These activities contribute to the increase in atmospheric $\mathrm{CO}_2$ levels, which can lead to global warming and climate change.

However, respiration (Option C) does not disturb the delicate balance of $\mathrm{CO}_2$ and $\mathrm{O}_2$. During respiration, organisms including humans and animals consume $\mathrm{O}_2$ and produce $\mathrm{CO}_2$ as a byproduct. This $\mathrm{CO}_2$ can be utilized by plants during photosynthesis to produce $\mathrm{O}_2$, thus maintaining a balance between $\mathrm{CO}_2$ and $\mathrm{O}_2$ levels in the atmosphere.

A - Steel plants : They generate waste in the form of slag (III), which is a by-product of the smelting process used in steel production.

B - Thermal power plants : These plants generate fly ash (II) as a by-product of coal combustion.

C - Fertilizer industries : The manufacture of phosphate fertilizers can produce gypsum (I) as a waste product.

D - Paper mills : They generate bio-degradable wastes (IV) as a result of the pulp and papermaking processes.

Therefore, the correct option is A : (A)-(III), (B)-(II), (C)-(I), (D)-(IV).

The breakdown of ozone in the stratosphere largely involves a series of reactions often initiated by free radicals, such as chlorine (Cl), bromine (Br), or nitric oxide (NO) radicals. In particular, chlorine atoms, which can come from substances like chlorofluorocarbons (CFCs), can catalyze the destruction of ozone.

The first three reactions listed are all part of the ozone breakdown process:

Option A: This is the photodissociation of a chlorofluorocarbon, which releases a chlorine atom (a free radical) that can participate in ozone destruction.

$\mathrm{CF_2Cl_2(g) \xrightarrow{uv} Cl(g) + CF_2Cl(g)}$

Option B: This reaction shows a chlorine atom catalyzing the destruction of ozone, forming ClO and O2.

$\mathrm{Cl(g) + O_3(g) \rightarrow ClO(g) + O_2(g)}$

Option D: This reaction shows a ClO radical reacting with a single oxygen atom to regenerate the Cl radical and form O2. The regenerated Cl radical can then go on to catalyze more ozone destruction, making this a catalytic cycle.

$\mathrm{ClO(g) + O(g) \rightarrow Cl(g) + O_2(g)}$

However, option C:

$\mathrm{2ClO \rightarrow ClO_2 + Cl}$

This reaction is not typically part of the ozone breakdown process. Chlorine monoxide (ClO) radicals generally react with atomic oxygen (O), not with another ClO radical, to regenerate the chlorine radical and produce oxygen (O₂). The product of this reaction, ClO₂, does not commonly appear in the standard ozone depletion mechanisms.

1. Fluoride ($F^-$) : High concentration of fluoride can lead to a condition known as fluorosis, affecting teeth and bones. Hence, the WHO sets the upper limit for fluoride in drinking water to be 1.5 ppm. This can be approximated to less than 2 ppm. Therefore, $F^-$ (List I: A) corresponds to < 2 ppm (List II: III).




2. Sulfate ($SO_4^{2-}$) : The standard concentration limit for sulphates in drinking water, according to WHO, is 500 ppm. Hence, $SO_4^{2-}$ (List I: B) matches with < 500 ppm (List II: IV).




3. Nitrate ($NO_3^-$) : An excess of nitrate in drinking water can lead to health conditions such as methemoglobinemia. The safe limit, according to the WHO, is 50 ppm. Hence, $NO_3^-$ (List I: C) corresponds to < 50 ppm (List II: I).




4. Zinc (Zn) : Zinc is an essential nutrient, but excessive amounts in drinking water can be harmful. The standard limit for zinc in drinking water is 5 ppm. So, Zn (List I: D) corresponds to < 5 ppm (List II: II).

Photochemical smog is a type of air pollution that results from the interaction between sunlight and pollutants such as nitrogen oxides and volatile organic compounds (VOCs). This type of smog is common in urban and industrial areas where there is a high concentration of these pollutants.

The conditions favorable for the formation of photochemical smog include strong sunlight, stagnant air, and the presence of pollutants such as those emitted by vehicles and industrial processes.

Given the options:

• Option A : Industrial areas - These typically have a high concentration of pollutants like nitrogen oxides and VOCs that can interact with sunlight to form photochemical smog.


• Option B : Himalayan villages in winter - Likely to have less sunlight and fewer pollutants.


• Option C : The places with healthy vegetation - Vegetation can actually help to reduce smog by absorbing pollutants.


• Option D : Marshy lands - Unlikely to have the concentration of pollutants necessary for photochemical smog formation.

The correct answer is : Option A : Industrial areas.

Option A (manufacturing of cement) is a significant contributor to global greenhouse gas emissions, as the production of cement releases large amounts of carbon dioxide (CO₂).

Option B (electricity generation in thermal power plants) is also a major contributor, as burning fossil fuels such as coal, natural gas, and oil to generate electricity releases large amounts of CO₂ and other greenhouse gases into the atmosphere.

Option C (steel manufacturing) also has a significant impact, as the production of steel requires high temperatures and the use of large amounts of energy, which can come from the burning of fossil fuels.

Option D (Industrial production of urea) has a lower impact compared to the other options, as it is a less energy-intensive process and does not directly release greenhouse gases into the atmosphere. However, the production of urea does rely on the use of natural gas as a feedstock, which does result in the release of some greenhouse gases.

Option A, By using catalytic converters in the automobiles/industry, is the most appropriate answer to control photochemical smog.

Photochemical smog is a type of air pollution that forms in urban areas when pollutants from automobile and industrial emissions, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), react in the presence of sunlight.

Catalytic converters are devices that are installed in the exhaust systems of automobiles and in some industrial processes to remove pollutants from exhaust gases. They work by using a catalyst to convert harmful pollutants, such as NOx and VOCs, into less harmful substances before they are released into the atmosphere. This can significantly reduce the formation of photochemical smog.

Option B, By complete combustion of fuel, is not a complete or sufficient solution to control photochemical smog. Complete combustion of fuel, which refers to the complete oxidation of the fuel to produce carbon dioxide and water, can reduce the amount of unburned hydrocarbons and carbon monoxide in the exhaust gases.

However, even with complete combustion, other pollutants, such as nitrogen oxides (NOx), can still be produced and contribute to the formation of photochemical smog. NOx emissions are a result of high temperatures and pressures in the combustion process and are not easily prevented through complete combustion alone.

Additionally, while complete combustion can reduce the amount of certain pollutants, it does not address other sources of pollution, such as industrial emissions, that can contribute to the formation of photochemical smog.

Therefore, while complete combustion can be an important step in reducing emissions and controlling photochemical smog, it is not a sufficient solution on its own and must be combined with other methods, such as the use of catalytic converters, to effectively address this issue.

Option C, using tall chimneys, is not a direct way to control photochemical smog. Tall chimneys can help to disperse pollutants into the atmosphere, but do not necessarily prevent their formation in the first place.

Option D, By using a catalyst, is not a complete or sufficient solution to control photochemical smog. While catalysts can be used to convert harmful pollutants into less harmful substances, they need to be part of a larger system, such as a catalytic converter, to effectively reduce emissions.

Using a catalyst alone, without the proper design, engineering, and installation, is unlikely to be effective in controlling photochemical smog. It is important to note that the goal is to reduce the overall emissions of pollutants, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), which are the precursors to photochemical smog.

Therefore, while catalysts can be a useful tool in controlling photochemical smog, they must be used in combination with other methods, such as the use of catalytic converters in automobiles and industry, to be most effective.

A clean water would have BOD value less than 5 ppm.

(i) $N{O_2}\buildrel {hv} \over \longrightarrow {{NO} \over {(A)}} + {O \over {(B)}}$

(ii) ${O \over {(B)}} + {O_2}\buildrel {} \over \longrightarrow {{{O_3}} \over {(C)}}$

(iii) ${{NO} \over {(A)}} + {{{O_3}} \over {(C)}}\buildrel {} \over \longrightarrow N{O_2} + {O_2}$

For high growth, dissolved oxygen should be less than 6 ppm and clean water has dissolved oxygen less than 5 ppm.