Key Concepts & Formulas

Provide 5-7 essential concepts for Environmental Issues:

10 Practice MCQs

Q1. Which gas is the primary contributor to greenhouse effect? A) Oxygen B) Carbon dioxide C) Nitrogen D) Hydrogen

Answer: B) Carbon dioxide

Solution:

• CO₂ constitutes 0.04% of atmosphere but responsible for 76% of greenhouse effect
• Other major gases: Methane (16%), Nitrous oxide (6%), Fluorinated gases (2%)

Shortcut: Remember “CO₂ = 76%” for greenhouse contribution

Concept: Environmental Issues - Greenhouse gases composition

Q2. The ozone layer is found in which atmospheric layer? A) Troposphere B) Stratosphere C) Mesosphere D) Thermosphere

Answer: B) Stratosphere

Solution:

• Ozone layer located 15-35 km above Earth’s surface
• Absorbs 97-99% of sun’s harmful UV-B radiation
• Maximum concentration at ~25 km altitude

Shortcut: “O-S-S” - Ozone in Stratosphere Saves us

Concept: Environmental Issues - Atmospheric layers

Q3. What is the ideal BOD value for clean water? A) 1-2 mg/L B) 5-10 mg/L C) 20-30 mg/L D) 50-100 mg/L

Answer: A) 1-2 mg/L

Solution:

• BOD <5 mg/L: Clean water
• BOD 5-15 mg/L: Moderately polluted
• BOD >15 mg/L: Heavily polluted
• Drinking water should have BOD <1 mg/L

Shortcut: “Lower is better” - Good water has <5 mg/L BOD

Concept: Environmental Issues - Water quality indicators

Q4. A train traveling 500 km consumes 25,000 liters diesel. If 1 liter produces 2.6 kg CO₂, what is the carbon footprint? A) 50 tons B) 65 tons C) 75 tons D) 85 tons

Answer: B) 65 tons

Solution:

• Total CO₂ = 25,000 × 2.6 = 65,000 kg
• Convert to tons: 65,000 ÷ 1,000 = 65 tons
• Carbon footprint = 65 tons CO₂

Shortcut: Liters × 2.6 ÷ 1000 = Tons of CO₂

Concept: Environmental Issues - Carbon footprint calculation

Q5. If Delhi’s PM2.5 level is 180 μg/m³ against WHO limit of 25 μg/m³, by what percentage is it exceeded? A) 440% B) 520% C) 620% D) 720%

Answer: C) 620%

Solution:

• Excess = 180 - 25 = 155 μg/m³
• Percentage excess = (155/25) × 100 = 620%
• Delhi’s level is 7.2 times the WHO limit

Shortcut: (Actual-Limit)/Limit × 100 = % Excess

Concept: Environmental Issues - Air quality standards

Q6. A railway station generates 2 tons waste/day. If 40% is biodegradable, how much methane produced annually? (1 ton waste = 100 kg methane) A) 29.2 tons B) 32.4 tons C) 36.5 tons D) 40.1 tons

Answer: A) 29.2 tons

Solution:

• Biodegradable waste = 2 × 0.4 = 0.8 tons/day
• Methane/day = 0.8 × 100 = 80 kg
• Annual methane = 80 × 365 = 29,200 kg = 29.2 tons

Shortcut: Waste × 0.4 × 100 × 365 ÷ 1000 = Annual methane tons

Concept: Environmental Issues - Waste to energy conversion

Q7. A factory buys 500 carbon credits at ₹200/credit. If each credit equals 1 ton CO₂ saved, what’s the total environmental benefit? A) ₹100,000 profit B) 500 tons CO₂ saved C) 200 MW power saved D) ₹10 lakh revenue

Answer: B) 500 tons CO₂ saved

Solution:

• 1 carbon credit = 1 ton CO₂ equivalent
• 500 credits = 500 tons CO₂ reduction
• This represents actual environmental benefit, not just monetary

Shortcut: Credits = Tons of CO₂ saved (direct 1:1 ratio)

Concept: Environmental Issues - Carbon trading mechanism

Q8. A 100-hectare forest absorbs CO₂ at 15 tons/hectare/year. If a railway line reduces it to 60 hectares, what’s the net CO₂ increase in atmosphere? A) 300 tons B) 400 tons C) 600 tons D) 900 tons

Answer: C) 600 tons

Solution:

• Original absorption = 100 × 15 = 1,500 tons/year
• New absorption = 60 × 15 = 900 tons/year
• Reduction in absorption = 1,500 - 900 = 600 tons/year
• This 600 tons extra CO₂ remains in atmosphere

Shortcut: Lost hectares × absorption rate = Extra CO₂

Concept: Environmental Issues - Deforestation impact

Q9. If India’s per capita carbon emission is 1.9 tons against world average of 4.8 tons, and population is 1.4 billion, what’s total annual emission? A) 1.96 billion tons B) 2.66 billion tons C) 3.25 billion tons D) 4.12 billion tons

Answer: B) 2.66 billion tons

Solution:

• Total emissions = Per capita × Population
• = 1.9 × 1.4 billion = 2.66 billion tons CO₂/year
• This is 7% of global total emissions

Shortcut: Per capita × population = Total (in same units)

Concept: Environmental Issues - National emission calculations

Q10. A coal-based power plant emits 0.98 kg CO₂/kWh. If Indian Railways consumes 2.5 billion kWh/year, what’s the carbon footprint? Give in million tons. A) 1.96 million tons B) 2.45 million tons C) 3.12 million tons D) 4.28 million tons

Answer: B) 2.45 million tons

Solution:

• Total CO₂ = 0.98 × 2.5 billion = 2.45 billion kg
• Convert to million tons: 2.45 billion ÷ 1,000 = 2.45 million tons
• This equals CO₂ absorption of 122 million trees/year

Shortcut: kWh × emission factor ÷ 1000 = Million tons CO₂

Concept: Environmental Issues - Large-scale carbon accounting

5 Previous Year Questions

PYQ 1. Which of the following is NOT a greenhouse gas? [RRB NTPC 2021 CBT-1]

Answer: C) Oxygen

Solution: Greenhouse gases: CO₂, CH₄, N₂O, water vapor, CFCs Oxygen (O₂) is not a greenhouse gas - it doesn’t trap heat

Exam Tip: Remember greenhouse gases are “CO-M-N-C” (CO₂, Methane, Nitrous oxide, CFCs)

PYQ 2. The depletion of ozone layer is mainly caused by: [RRB Group D 2022]

Answer: A) Chlorofluorocarbons (CFCs)

Solution:

• CFCs release chlorine atoms that destroy ozone molecules
• 1 chlorine atom can destroy 100,000 ozone molecules
• Main sources: Refrigerators, aerosol sprays, foam packaging

Exam Tip: “CFC destroys O3” - remember both have 3 letters but CFC is harmful

PYQ 3. What is the safe limit of PM2.5 as per WHO guidelines? [RRB ALP 2018]

Answer: B) 25 μg/m³

Solution: WHO guidelines:

• PM2.5: 25 μg/m³ (24-hour mean)
• PM10: 50 μg/m³ (24-hour mean)
• India’s standard: 60 μg/m³ for PM2.5

Exam Tip: Remember “2-5” for PM2.5 limit = 25 μg/m³

PYQ 4. Which pollutant causes Minamata disease? [RRB JE 2019]

Answer: C) Mercury

Solution:

• Minamata disease: Mercury poisoning from fish consumption
• First identified in Minamata Bay, Japan (1956)
• Affects nervous system, causes birth defects

Exam Tip: “Mercury-Minamata” - both start with ‘M’

PYQ 5. The Earth Summit 1992 was held at: [RPF SI 2019]

Answer: A) Rio de Janeiro

Solution:

• Official name: UN Conference on Environment and Development
• Key outcomes: Agenda 21, Climate Change Convention
• Led to Kyoto Protocol (1997) and Paris Agreement (2015)

Exam Tip: “Rio-92” - remember both numbers: 1992

Speed Tricks & Shortcuts

For Environmental Issues, provide exam-tested shortcuts:

Common Mistakes to Avoid

Quick Revision Flashcards

Topic Connections

How Environmental Issues connects to other RRB exam topics:

• Direct Link: Geography - Climate zones, atmospheric layers, pollution hotspots
• Combined Questions: Chemistry - Greenhouse gases, acid rain chemistry, ozone reactions
• Foundation For: Current Affairs - COP summits, environmental policies, climate targets
• Calculation Link: Math - Carbon footprints, emission reductions, percentage exceedances
• Application Link: Physics - Solar panels, wind energy, emission control technologies