Vidaara.orgClass 11 · Chemistry
CodeVID-C11-14-T2-01
Assignment — Water & Soil Pollution
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Interpret data carefully where given. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
BOD stands for:
- A.Biochemical Oxygen Demand
- B.Basic Oxide Demand
- C.Bacterial Organic Decay
- D.Boiling Oxygen Drop
2.
Which disease can be caused by water-borne pathogens?
- A.Fluorosis
- B.Typhoid
- C.Global warming
- D.Acid rain
3.
Eutrophication directly leads to:
- A.an increase in dissolved oxygen
- B.depletion of dissolved oxygen
- C.a fall in temperature
- D.removal of all nutrients
4.
The recommended maximum fluoride level in drinking water is about:
- A.1 ppm
- B.50 ppm
- C.500 ppm
- D.5000 ppm
5.
Organomercury compounds are used as:
- A.insecticides
- B.herbicides
- C.fungicides
- D.fertilisers
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Define Biochemical Oxygen Demand (BOD) and state how it relates to water quality.
7.
Name three causes of water pollution with one example each.
8.
Why are nitrates in drinking water harmful to infants?
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Explain the process of eutrophication step by step.
10.
Classify pesticides into three types based on target organisms, giving an example of each.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Discuss water pollution: its main causes, the meaning and significance of dissolved oxygen and BOD, the role of international drinking-water standards, and how eutrophication damages aquatic ecosystems.
Answer Key
Section A — Multiple Choice Questions
- (A) Biochemical Oxygen Demand
- (B) Typhoid
- (B) depletion of dissolved oxygen
- (A) 1 ppm
- (C) fungicides
Section B — Short Answer (2 marks)
- BOD is the amount of oxygen (mg/L) needed by microorganisms to decompose the organic matter in one litre of water; higher BOD means more organic pollution and poorer water quality.
- Pathogens (e.g. bacteria from sewage), biodegradable organic wastes (e.g. food/plant waste), and inorganic chemicals (e.g. nitrates/heavy metals from industry).
- Excess nitrate (above ~50 ppm) causes methaemoglobinaemia or 'blue baby' syndrome, reducing the blood’s ability to carry oxygen.
Section C — Short Answer (3 marks)
- Fertiliser run-off adds nitrates and phosphates to water; these nutrients cause rapid algal growth (algal bloom); when the algae die, bacterial decay consumes the dissolved oxygen, killing fish and aquatic life.
- Insecticides kill insects (e.g. DDT); herbicides kill weeds (e.g. sodium chlorate or triazines); fungicides kill fungi (e.g. organomercury compounds).
Section D — Long Answer (5 marks)
- Causes: pathogens from sewage, biodegradable organic wastes, and toxic inorganic/chemical wastes (heavy metals, nitrates, phosphates). DO is the oxygen dissolved in water (~8–10 mg/L in clean water) needed by aquatic life; BOD is the oxygen microbes need to decompose organic matter, so high BOD signals heavy pollution and low DO. Standards (WHO/BIS) cap contaminants (fluoride ~1 ppm, nitrate ~50 ppm, lead ~50 ppb) to protect health. Eutrophication: nutrient run-off causes algal blooms; their decay depletes oxygen, suffocating fish and degrading the ecosystem.
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