Concept Notes (Deep Explanation + Examples)
🔹 What is Pollution?
Pollution is the unwanted change in the physical, chemical, or biological characteristics of air, water, or soil that adversely affects living organisms and the environment.
In ECET exams, questions often appear about pollutants, their sources, and chemical reactions involved.
🌫️ Air Pollution
Air pollution occurs when harmful gases and particles mix with the atmosphere.
It mainly comes from industries, vehicles, and burning of fossil fuels.
🔸 Major Air Pollutants
| Type | Example | Effect |
|---|---|---|
| Gaseous | CO, NO₂, SO₂, hydrocarbons | Respiratory issues, acid rain |
| Particulate | Dust, smoke, ash | Smog, lung diseases |
🔹 Common Air Pollutants and Their Effects
- Carbon Monoxide (CO):
Produced by incomplete combustion of fuels.
Combines with hemoglobin forming carboxyhemoglobin, reducing oxygen transport.
- Sulphur Dioxide (SO₂):
Comes from burning coal or oil.
Reacts with water vapor forming sulfuric acid, causing acid rain.
Nitrogen Oxides (NO, NO₂):
Produced from automobile engines.
Causes photochemical smog and acid rain.
Hydrocarbons:
Unburnt fuels; contribute to smog formation.
🔹 Effects of Air Pollution
- Respiratory diseases (asthma, bronchitis)
- Global warming (CO₂ accumulation)
- Acid rain damaging monuments (e.g., Taj Mahal)
- Depletion of ozone layer
🧪 Real-world example:
In cities like Delhi, AQI (Air Quality Index) crosses 400 due to vehicle emissions. Students studying near industrial zones often notice irritation in eyes — a clear symptom of high SO₂ and NO₂ in the air.
💧 Water Pollution
Water pollution occurs when undesirable chemicals enter lakes, rivers, or groundwater.
These pollutants reduce oxygen levels and harm aquatic life.
🔸 Major Causes of Water Pollution
- Domestic Waste:
Sewage, detergents, food residues. - Industrial Waste:
Heavy metals (Pb, Hg, Cr), acids, dyes. - Agricultural Waste:
Pesticides, fertilizers (nitrates, phosphates).
🔹 Types of Water Pollutants
| Type | Example | Effect |
|---|---|---|
| Organic | Urea, phenol, detergents | Deplete dissolved oxygen |
| Inorganic | Nitrates, phosphates, metals | Toxic to aquatic life |
| Biological | Bacteria, viruses | Cause water-borne diseases |
🔹 Key Concepts
1. Biochemical Oxygen Demand (BOD):
Amount of oxygen required by microorganisms to decompose organic matter.
→ Higher BOD = More polluted water
2. Chemical Oxygen Demand (COD):
Oxygen required to oxidize organic & inorganic matter chemically.
3. Eutrophication:
Overgrowth of algae due to excess nutrients (nitrates, phosphates). Reduces oxygen and kills aquatic life.
4. Thermal Pollution:
Hot water from industries increases temperature → reduces oxygen solubility.
🧠 ECET TIP
“BOD, COD, and Acid Rain reactions are repeated every year in ECET Chemistry.”
🔹 Real-world Example
- Industrial discharge in rivers like Ganga and Krishna increases BOD drastically.
- Fish deaths reported due to eutrophication and low oxygen levels.
🔹 Diagram Explanation (in words)
Imagine a flow diagram:
Factories → Chemical discharge → River → Increased BOD → Algae bloom → Oxygen depletion → Fish death.
This is the typical process of water pollution as asked in exams.
4️⃣ 🔟 10 MCQs (ECET + GATE Hybrid)
- Which gas is mainly responsible for acid rain?
A) CO
B) SO₂
C) CH₄
D) NH₃ - BOD is a measure of:
A) Organic matter in water
B) Temperature of water
C) Hardness of water
D) pH of water - The main cause of photochemical smog is:
A) CO₂
B) SO₂
C) Hydrocarbons and NOₓ
D) CFCs - Which metal is most toxic in water pollution?
A) Iron
B) Lead
C) Calcium
D) Sodium - COD is:
A) Biological parameter
B) Chemical parameter
C) Physical parameter
D) None - Which of the following increases BOD?
A) Cold temperature
B) Organic waste
C) Less bacteria
D) Pure water - The main pollutant from vehicles is:
A) CO
B) SO₂
C) NH₃
D) CH₄ - The ozone layer protects us from:
A) Infrared radiation
B) UV radiation
C) Visible light
D) Gamma rays - Eutrophication is caused by excess:
A) Sulphur compounds
B) Phosphates and nitrates
C) CO₂
D) Ammonia - Acid rain is caused by the presence of:
A) NO₂ and SO₂
B) CO₂ and CH₄
C) H₂ and O₂
D) CO and NH₃
5️⃣ ✅ Answer Key (WordPress Table — NO HTML)
Q No | Answer
1 | B
2 | A
3 | C
4 | B
5 | B
6 | B
7 | A
8 | B
9 | B
10 | A
6️⃣ 🧠 MCQ Explanations
1️⃣ SO₂ forms sulfuric acid → acid rain.
2️⃣ BOD measures organic pollution by oxygen demand.
3️⃣ NOₓ + Hydrocarbons react under sunlight → smog.
4️⃣ Lead (Pb) is highly toxic, causing neurological issues.
5️⃣ COD uses dichromate to measure total oxidizable matter (chemical test).
6️⃣ More organic waste → more bacteria → higher BOD.
7️⃣ Vehicles emit CO due to incomplete fuel burning.
8️⃣ Ozone absorbs UV rays, protecting living beings.
9️⃣ Excess fertilizers lead to algae growth (eutrophication).
10️⃣ Both SO₂ and NO₂ form acids causing acid rain.
7️⃣ 🎯 Motivation (ECET 2026 Specific)
“Every year, ECET Chemistry paper includes 1–2 direct questions from Pollution topics (BOD, acid rain, smog).
Understanding these concepts not only helps in ECET but also improves your awareness of environmental chemistry.
Stay consistent — small daily learning leads to big rank jumps!”
8️⃣ 📲 CTA (Fixed)
Join our ECET 2026 CSE WhatsApp Group for daily quizzes & study notes:
https://chat.whatsapp.com/GniYuv3CYVDKjPWEN086X9
