Gases

Introduction

A gas is a state of matter with no fixed shape or volume.
Gas molecules are far apart, move freely, and can expand to fill any container.
Many essential gases—like oxygen, carbon dioxide, methane—play major roles in breathing, burning, environment, and industry.

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Properties of Gases

• Highly compressible
• No fixed volume or shape
• Exert pressure equally in all directions
• Diffusion and expansion are rapid
• Obey Gas Laws: Boyle’s Law, Charles’s Law, Ideal Gas Law

📝 PYQ (BPSC): Which property is not shown by solids but shown by gases? → Compressibility
📝 Expected MCQ: Which law states pressure is inversely proportional to volume? → Boyle’s Law

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Common Gases and Their Uses

📝 Expected MCQ: Which gas is used in fire extinguishers? → Carbon dioxide
📝 Expected MCQ: Most abundant gas in air? → Nitrogen

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Gases Important for Life

✔️ Oxygen (O₂)

• Vital for respiration in humans and animals
• Used in hospitals, oxygen cylinders
• Supports combustion

✔️ Carbon Dioxide (CO₂)

• Used by plants for photosynthesis
• Excess CO₂ → global warming
• Used in aerated drinks

✔️ Nitrogen (N₂)

• 78% of Earth’s atmosphere
• Used in making urea, ammonium nitrate

📝 PYQ (BPSC): Which gas is essential for plant photosynthesis? → Carbon dioxide

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Polluting and Dangerous Gases

• Carbon Monoxide (CO): Produced by incomplete burning, toxic to humans
• Sulphur Dioxide (SO₂) and Nitrogen Oxides (NOx): Cause acid rain
• Methane (CH₄): Greenhouse gas, explosive
• CFCs: Cause ozone layer depletion

📝 PYQ (CDPO): Which gas is released during incomplete combustion? → Carbon monoxide
📝 Expected MCQ: Ozone depletion is caused by? → CFCs

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Bihar-Specific Relevance

🌾 Biogas Plants

• Methane produced in rural biogas units used for cooking
• Supported by Bihar’s renewable energy and rural sanitation schemes

🌆 Urban Air Pollution

• Carbon monoxide, PM2.5, and NOx rise due to vehicles and open burning
• Patna often shows high Air Quality Index (AQI)

🧪 Industrial Use

• Ammonia used in fertilizer plants (e.g., Barauni Fertilizer Complex)
• Nitrogen used for food storage in Bihar’s dairy and agro units

📝 Expected MCQ: Biogas mainly contains? → Methane
📝 Expected MCQ: Which gas causes maximum urban pollution in Bihar? → Carbon monoxide

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Gas Laws – Quick Concepts

• Boyle’s Law: P ∝ 1/V (at constant T)
• Charles’s Law: V ∝ T (at constant P)
• Ideal Gas Law: PV = nRT

📝 Expected MCQ: Which law is related to pressure and volume? → Boyle’s Law

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Gases in the Atmosphere (by volume)

• Nitrogen (78%), Oxygen (21%), Argon (~1%), CO₂ (~0.04%)
• Trace gases: Neon, Helium, Methane, Ozone, etc.

📝 Expected MCQ: Which gas is present in highest amount in air? → Nitrogen

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PYQs + Expected MCQs

📝 PYQ (BPSC): Which gas supports combustion? → Oxygen
📝 PYQ (CDPO): Which gas is harmful and formed by incomplete burning? → Carbon monoxide
📝 Expected MCQ: Which gas causes acid rain? → Sulphur dioxide
📝 Expected MCQ: What is the percentage of oxygen in the atmosphere? → 21%
📝 Expected MCQ: Gas used in fertilizer production? → Ammonia

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Quick Revision Points

• Gases have no fixed shape or volume, compressible
• Major air gases: N₂, O₂, Ar, CO₂
• O₂ supports life; CO₂ for plants; CO = poison
• Gases involved in air pollution: CO, NO₂, SO₂, CH₄
• Bihar: Biogas → CH₄; pollution → CO, PM2.5
• Boyle’s Law: P ∝ 1/V; Charles’s Law: V ∝ T

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Sources Used

• NCERT Science Class 9–10
• Lucent GK – Chemistry & Environment Section
• Drishti Science Quick Book
• EduTeria + Ghatna Chakra PYQs (BPSC, CDPO, DPRO)
• BSPCB – Bihar State Pollution Control Reports
• BREDA – Bihar Renewable Energy Updates
• MoEFCC – AQI & Climate Reports