Environmental Chemistry — NEET UG practice

1. Understand the correct meaning of eutrophication before evaluating Statement I.

Eutrophication is a process where a water body becomes excessively enriched with nutrients (such as phosphates and nitrates), usually from agricultural runoff or sewage, leading to explosive growth of algae and other plants.

2. Evaluate Statement I against this definition.

Statement I claims that nutrient-deficient water bodies lead to eutrophication, but this is the opposite of the truth — it is nutrient-rich water bodies that undergo eutrophication. So Statement I is incorrect.

3. Evaluate Statement II by considering what happens after excessive algal growth.

When the algae and plants from eutrophication eventually die, they are decomposed by bacteria, which consume dissolved oxygen in the water in large amounts. This leads to a decrease in oxygen levels, harming fish and other aquatic organisms (a condition called hypoxia). So Statement II is true.

4. Combine the two conclusions.

Since Statement I is false and Statement II is true, the correct choice reflects this combination.

Hence, the answer is C.

1. Recall what photochemical smog is and what it affects.

Photochemical smog is a type of air pollution formed when sunlight acts on pollutants like nitrogen oxides and hydrocarbons, producing harmful secondary pollutants such as ozone and peroxyacetyl nitrate (PAN).

2. Check whether photochemical smog affects only humans or also plants.

Photochemical smog is known to damage plant tissues and interfere with plant growth, in addition to harming human health (causing eye and throat irritation, breathing problems, etc.). So the claim that it "has no effect on plants" is factually incorrect.

3. Verify the other statements briefly.

• Certain plants like Pinus and Juniperus are indeed known to help reduce photochemical smog by absorbing pollutants.
• Photochemical smog does occur in warm, dry, sunny climates, since sunlight is essential for the photochemical reactions.
• The common components listed (ozone, nitric oxide, acrolein, formaldehyde, PAN) are indeed typical of photochemical smog.

4. Conclude which statement is false.

Since photochemical smog does affect plants, the statement claiming it has "no effect on plants" is not true.

Hence, the answer is A.

1. Match (a) Biochemical oxygen demand (BOD) with its correct meaning.

BOD measures the amount of oxygen required by microorganisms to decompose the organic matter present in water. So:

$$\text{(a) Biochemical oxygen demand} \rightarrow \text{(iii) organic matter in water}$$

2. Match (b) Photochemical smog with its chemical character.

Photochemical smog contains components like ozone and PAN, which are strong oxidising agents. So:

$$\text{(b) Photochemical smog} \rightarrow \text{(i) oxidising mixture}$$

3. Match (c) Classical smog with its chemical character.

Classical smog (formed from smoke and fog with sulphur dioxide) behaves as a reducing mixture, unlike the oxidising photochemical smog. So:

$$\text{(c) Classical smog} \rightarrow \text{(iv) reducing mixture}$$

4. Match (d) Ozone layer depletion with the relevant atmospheric phenomenon.

Ozone depletion, especially over polar regions, is closely linked to the formation of polar stratospheric clouds, which provide surfaces for reactions that destroy ozone. So:

$$\text{(d) Ozone layer depletion} \rightarrow \text{(ii) polar stratospheric cloud}$$

5. Combine all the matches.

This gives (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii).

Hence, the answer is D.