Chemistry of Gases and Applications

Biogas is primarily composed of methane (CH4), which typically makes up 50-75% of the gas mixture. Methane is the main combustible component that gives biogas its energy value. Option A correctly identifies methane as the chief constituent. Option B (hydrogen) is present only in trace amounts. Option C represents ethyl alcohol, which is not a component of biogas. Option D (CO2) is present as a non-combustible component (30-40%) but is not the chief constituent.

Hydrogen gas has the highest calorific value among all fuels at approximately 142 kJ/g, significantly higher than methane (~55 kJ/g), ethane (~52 kJ/g), or biogas (~20-25 kJ/g). Option B correctly identifies hydrogen as having the highest calorific value. Option A (methane) has a high calorific value but not the highest. Options C and D have lower calorific values compared to hydrogen.

Calorific value of LPG = 55,000 kJ/kg   Calorific value of biogas = 35000-40000 kJ/kg Calorific value of hydrogen = 1,50,000 kJ/kg

Coal gas, also known as town gas, was historically used primarily for illumination (lighting) in homes and street lamps before the widespread adoption of electricity. Option A correctly identifies this historical use. Disinfection (B) requires different gases. Deep freezing (C) uses refrigerants. Chemical preservation (D) is not a primary application of coal gas. The illuminating property of coal gas made it valuable for lighting applications.

Carbon monoxide (CO) is highly poisonous because it binds to hemoglobin in red blood cells 200+ times more strongly than oxygen, preventing oxygen transport and causing asphyxiation. CO2 is not poisonous in normal concentrations but causes suffocation by displacing oxygen. Nitrogen is inert.

Dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide and small amounts of other gases. Air also contains a variable amount of water vapour on average around 1%. In fact, air contains slightly less than 1% argon making it the third most abundant gas in air after nitrogen and oxygen. Argon is the most abundant and most used of the noble gases.

For combustion to occur (that is a fire to start), oxygen must be present. Fire is a chemical reaction that creates light and heat from oxygen and fuel. A lit candle needs to draw oxygen from the air in order to continue burning. If you limit the amount of air available, the candle's flame eventually goes out once it uses up all the oxygen. When a candle burns, the wax is reacting with oxygen in the air to give out heat and light. If you give the candle more oxygen, then it will burn brighter but it will burn out more quickly. It all depends whether the candle has a high or low concentration of oxygen.

When you breathe in, nitrogen gas will enter the blood and circulate around the body without being used up or added to. When it reaches the lungs, it will pass out again. The percentage of nitrogen inhaled is roughly 79% but it is only 74% when exhaled. Nitrogen is a rather inert gas that does not change density depending on temperature as readily as oxygen does. Nitrogen itself is not actually used up by the body. It is simply a byproduct of the nitrates and various emissions involved in photosynthesis from plants and various algae that get pumped with whimsical abandon into the atmosphere.

Methane is a compound and its elements are combined in fixed proportion.

Petrol in diesel is a homogeneous mixture.

It is a homogeneous and a solid-liquid mixture.

Producer gas is CO + N₂. The core of lead pencil is made of non-toxic graphite and does not contain lead.

The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn).

Oxides of Sulphur cause breathing infection.

 Refrigerator, fire extinguisher and air conditioner emit CFCs in large quantities whereas DC motors do not emit CFCs.