Environmental Chemistry

$\mathrm{CO}_2$ (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.

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.

Coldest layer of Earth’s atmosphere is mesosphere which in directly above the stratosphere and below thermosphere so, temperature at this layer is $-90^\circ$C.

Greenhouse gases include water vapour, CO$_2$, CH$_4$, nitrous oxide, O$_3$ and CFC. The absorbed energy warms the atmosphere and the surface of the Earth.

SO$_2$ (sulphur dioxide) is not a greenhouse gas.

The main component of photochemical smog is peroxy acetyl nitrate (PAN).

There are three components involved ozone, nitric acid acrolin and formaldehyde.

The main component of oxidising smog or photochemical smog is PAN.

Green chemistry contains twelve principles and it is the approach in chemical sciences that efficiently uses renewable raw materials, eliminating waste and avoiding the use of toxic and hazardous reagents.

It is the use of chemistry for pollution prevention by an environmentally conscious design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances.