Chapter Exam

Chapter 8: Environmental Issues — Online MCQ Test

Q: Which of the following units is used to measure the thickness of the ozone layer in a column of air?

Answer: B. Dobson Unit (DU) — The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson Units (DU).

Q: In which year did the Government of India pass the Environment (Protection) Act to protect and improve the quality of our environment?

Answer: C. 1986 — The Environment (Protection) Act was passed in the year 1986 by the Government of India to protect and improve the quality of air, water, and soil.

Q: Read the following statements regarding eutrophication: 1. It is the natural aging of a lake by nutrient enrichment. 2. Run-off from agricultural fields containing nitrates and phosphates accelerates this process. 3. It leads to an increase in dissolved oxygen, favoring fish growth. Which of the statements given above is/are CORRECT regarding 'cultural eutrophication'?

Answer: B. 2 only — Cultural eutrophication is the human-accelerated (anthropogenic) aging of water bodies. It depletes dissolved oxygen because decomposers consume it all, leading to fish mortality, making only Statement 2 correct.

BOTANY · CLASS 12th · Tamil Nadu State Board

Practice Chapter 8: Environmental Issues with a free chapter-wise online MCQ test for Tamil Nadu State Board CLASS 12th BOTANY. This chapter covers: Focusing on environmental conservation this chapter covers air water and soil pollution hazards. Students study greenhouse effect climate change ozone layer depletion deforestation.... AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter 8: Environmental Issues — Important Questions & Answers (FAQ)

Frequently asked questions from Tamil Nadu State Board CLASS 12th BOTANY — Chapter 8: Environmental Issues, with answers and explanations. These are sample questions; the exam has its own separate question set.

Which of the following units is used to measure the thickness of the ozone layer in a column of air?

A. Decibel (dB)
B. Dobson Unit (DU) ✓
C. Parts per million (ppm)
D. Nanometer (nm)

Answer: B. Dobson Unit (DU)
The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson Units (DU).

In which year did the Government of India pass the Environment (Protection) Act to protect and improve the quality of our environment?

A. 1974
B. 1981
C. 1986 ✓
D. 1988

Answer: C. 1986
The Environment (Protection) Act was passed in the year 1986 by the Government of India to protect and improve the quality of air, water, and soil.

A water body with a very high Biochemical Oxygen Demand (BOD) value indicates that:

A. The water is highly pure and contains minimal dissolved minerals.
B. The water is highly polluted with organic matter. ✓
C. There is an abundance of dissolved oxygen for aquatic organisms.
D. The water is completely free of microbial activity.

Answer: B. The water is highly polluted with organic matter.
A high BOD value indicates that microorganisms require a large amount of oxygen to decompose organic waste, which points to severe organic pollution.

Read the following statements regarding eutrophication: 1. It is the natural aging of a lake by nutrient enrichment. 2. Run-off from agricultural fields containing nitrates and phosphates accelerates this process. 3. It leads to an increase in dissolved oxygen, favoring fish growth. Which of the statements given above is/are CORRECT regarding 'cultural eutrophication'?

A. 1 and 2 only
B. 2 only ✓
C. 2 and 3 only
D. 1, 2 and 3

Answer: B. 2 only
Cultural eutrophication is the human-accelerated (anthropogenic) aging of water bodies. It depletes dissolved oxygen because decomposers consume it all, leading to fish mortality, making only Statement 2 correct.

During the depletion of the stratospheric ozone layer, Chlorofluorocarbons (CFCs) are broken down by ultraviolet (UV) radiation. What is the role of the released Chlorine atoms in this pathway?

A. They act as reactants and are completely consumed in converting ozone to oxygen.
B. They act as catalysts, meaning they are not consumed in the reaction and can continuously degrade ozone. ✓
C. They bind with oxygen molecules to form stable chlorine oxides, reducing UV radiation absorption.
D. They react with nitrous oxide to neutralize the greenhouse effect in the troposphere.

Answer: B. They act as catalysts, meaning they are not consumed in the reaction and can continuously degrade ozone.
Chlorine atoms act as catalysts in the stratosphere; they convert ozone into oxygen without being consumed, allowing a single chlorine atom to destroy thousands of ozone molecules.