Fuels and Combustion

Lignite coal has a high moisture content in the range of 45% to 55%.

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.

Biogas is produced through anaerobic digestion of organic matter known as biomass. Biomass includes agricultural waste, animal dung, sewage, and other organic materials. Option D correctly identifies biomass as the raw material for biogas production. Options A (petrol), B (kerosene), and C (minerals) are all incorrect as they are fossil fuels or inorganic substances that cannot produce biogas through biological processes.

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.

The luminous (yellow) zone of a flame contains unburnt carbon particles that glow due to incomplete combustion. These carbon particles are formed when hydrocarbon fuels don't fully combust due to limited oxygen supply. Option C correctly identifies the luminous zone. The blue zone (A) has complete combustion with no unburnt carbon. The dark inner zone (B) is the coolest region with unburnt fuel vapors. The non-luminous zone (D) is the blue outer zone.

Combustion is fundamentally an oxidation reaction where a substance combines with oxygen, releasing energy in the form of heat and light. Option A correctly identifies it as oxidation. Reduction (B) is the opposite process involving gain of electrons. Neutralization (C) refers to acid-base reactions. Combustion is distinctly characterized by rapid oxidation with accompanying energy release.

 The gas obtained during destructive distillation of coal is  coal gas .

Burning kerosene oil is classified as rapid combustion because it occurs at a fast rate when the fuel is ignited, producing heat and light steadily. Option A correctly identifies this as rapid combustion. Spontaneous combustion (B) occurs without external ignition. Explosion (C) involves sudden, violent combustion with pressure waves. Kerosene burning is a controlled, steady burning process, not an explosion.

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

LPG (liquefied petroleum gas) used as a domestic fuel has a high calorific value. The ignition temperature of this fuel is reasonably low. It is a mixture of hydrocarbons.

The cooking gas used as a fuel for domestic purposes is liquified petroleum gas.

Primary fuels or primary energy sources are dense sources of primary energy found as natural resources. Primary fuels are fuels that are found in nature and can be extracted, captured, cleaned or graded without any sort of energy conversion or transformation process.

Wood has a calorific value of approximately 17 kJ/g, which falls within the typical range of 15-20 kJ/g for dry wood. Option B correctly states this value. Option A (33 kJ/g) is too high and closer to coal. Option C (3.7 kJ/g) is far too low. Option D (1.7 kJ/g) is unrealistically low for wood. The 17 kJ/g value represents the average energy content of good quality dry wood fuel.

In villages and rural areas, wood is the most commonly used naturally occurring solid fuel for cooking and heating. Option B correctly identifies wood as the primary rural solid fuel. Coal (A) is also used but less commonly in villages due to cost and availability. Paraffin (C) is a liquid fuel, not solid. Coke (D) is a processed coal product, not naturally occurring, and is less commonly used in village settings.

Anthracite is a hard, compact variety of coal that has a sub-metallic lustre. It has the highest carbon content, the fewest impurities and the highest calorific content of all types of coal. The carbon content is between 92.1% - 98% . In lignite, the carbon content is 25-35%. Bituminous contains 60-80% carbon. In peat, the carbon content is less than 60%.

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.

Petroleum is a mixture of hydrocarbons.

Petroleum is separated into different parts by the process of fractional distillation.

Smokeless chulhas are specially designed stoves that efficiently burn wood while minimizing smoke production through improved airflow and combustion design. Option A correctly identifies smokeless chulhas. Ordinary chulhas (C) produce significant smoke. Hearths (B) are traditional fireplaces without smoke reduction features. Smokeless chulhas are promoted for better health and environmental outcomes.

Liquefied Petroleum Gas (LPG) is classified as a gaseous fuel that has been liquefied under pressure for storage and transportation. In its normal state at atmospheric pressure, LPG exists as a gas (propane and butane). Option C correctly identifies it as a gaseous fuel. Option A (solid fuel) is incorrect. Option B (liquid fuel) describes its storage form, not its fundamental classification. Option D is false as LPG is indeed a fuel.

Coal gas is produced by destructive distillation of coal and contains a mixture of gases. The primary components are hydrogen (H2), methane (CH4), and carbon monoxide (CO). Option A only lists two components, while option B correctly lists all three major constituents of coal gas.

The gas obtained during destructive distillation of coal is coal gas. 

Petroleum refining involves separating crude oil into its various components based on their boiling points. This separation technique is called fractional distillation. Carbonisation refers to converting coal to coke, while destructive distillation is used for coal gas production.

Passing steam over red hot coke (carbon) produces a mixture of carbon monoxide and hydrogen, which is known as water gas. Producer gas is made by passing air over red hot coke instead.

Biogas has a higher calorific value (approximately 35-40 MJ/m³) compared to dung cakes (approximately 10-15 MJ/kg). This means biogas produces more heat per unit mass, making it more efficient as a fuel. The other options either don't explain why it's better (availability, ease of burning) or state the opposite (incomplete combustion).

Anthracite is the highest grade coal with the highest carbon content (86-97%) and burns with the hottest, most consistent flame, making it ideal for thermal power plants. Bituminous coal is also used but anthracite is preferred for its superior energy content and cleaner burn.

A good fuel should have high calorific value to provide maximum energy. Low ignition temperature would be dangerous (fuel could ignite too easily). High oxygen content is not desirable as it reduces the energy density. Therefore, high calorific value is the correct characteristic.

LPG (Liquefied Petroleum Gas) is primarily composed of butane and propane. While propane is a significant component, butane is the major constituent in most commercial LPG mixtures. Methane is the main component of natural gas (CNG), not LPG. Pentane is less common in LPG formulations.

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.

Methane (CH4) has the highest calorific value among the options (55 MJ/kg). Hydrogen has the highest of all fuels (142 MJ/kg) but isn't listed. Coal and wood have much lower calorific values than gaseous fuels like methane. Dung cakes have the lowest calorific value among common fuels.

Biogas typically contains 50-75% methane, with 60-65% being the most common range for well-operating biogas plants. The balance is mostly CO2 (30-40%) with small amounts of other gases. Option B (65%) falls within this typical range and is the correct answer.

Coal gas is produced when coal is heated strongly in the absence of air during destructive distillation. This process breaks down the complex coal molecules, releasing volatile components that form coal gas, which contains hydrogen, methane, and carbon monoxide.

Percentage of carbon in anthracite coal is in between 92.1% and 98%.

A hydrocarbon is an organic chemical compound consisting entirely of two elements, namely hydrogen and carbon. They form the basis of petroleum, natural gas, and coal.

Hydrogen has the highest calorific value among common fuels, approximately 150 kJ/g. This is because hydrogen forms water (H₂O) upon combustion, releasing a large amount of energy per gram due to its low atomic mass and strong bond formation.

In petroleum refining, crude oil is heated in a furnace to about 400 degrees Celsius before being fed into the base of a fractional distillation column to vaporize its components.

Fossil fuels like coal, petroleum, and natural gas are primarily composed of hydrocarbons - compounds containing only carbon and hydrogen atoms. These hydrocarbons store energy that is released during combustion.

Rocket fuel is specifically called propellant, which includes both fuel and oxidizer components needed for combustion in space where there is no air. Solid propellants and liquid propellants are the two main types used in rockets.

Fractional distillation is used for refining petroleum because of hydrogen fractions which have different boiling temperatures.

Carbon tetrachloride (CCl₄) is a dense, non-flammable liquid that effectively extinguishes fires by smothering flames and displacing oxygen. It was historically used for electrical and oil fires because it does not conduct electricity and forms a heavy vapor blanket.

Fossil fuels are formed from the remains of ancient plants and animals that originally captured solar energy through photosynthesis millions of years ago. Therefore, the ultimate source of energy stored in fossil fuels is the sun.

Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane (CH4), along with varying amounts of higher alkanes and small percentages of other gases.

The process by which one type of petroleum oil is converted into another type is called cracking.

Burning fossil fuels releases carbon dioxide, carbon monoxide, nitrogen oxides, sulfur dioxide, and particulate matter into the atmosphere. These emissions contribute significantly to air pollution, causing smog, acid rain, and health problems. They do not directly cause water, soil, or sound pollution.

Photosynthesis is the process by which green plants use sunlight to convert carbon dioxide and water into glucose (food) and oxygen. Chlorophyll in plant cells captures solar energy to drive this reaction, which is the foundation of most food chains on Earth.

Coal tar is a complex mixture containing hundreds of different organic compounds, primarily aromatic hydrocarbons like benzene, toluene, xylene, and naphthalene. It is produced during the destructive distillation of coal and is definitely not a single compound or element.

The ignition temperature is the lowest temperature at which a combustible substance catches fire in the air. Boiling point refers to phase change to vapor, and oxidation is a chemical reaction type.

Coal was formed from the trees (fossils) that got buried under the layers of the earth during natural calamities like earthquake etc.
Under geothermal conditions of high temperature and pressure, wood is converted into coal. 

A candle flame has three distinct zones: (1) Inner dark zone - incomplete combustion due to insufficient oxygen, (2) Middle luminous zone - moderate combustion with yellow glow, and (3) Outer non-luminous zone - complete combustion with blue flame. This three-zone structure is characteristic of hydrocarbon flames.

Conventional energy sources are those that have been traditionally used for centuries, like wood, agricultural waste, cow dung (biomass). Non-conventional sources are newer or renewable alternatives like wind, solar, tidal, geothermal. Wind is classified as non-conventional renewable energy.

LPG (Liquefied Petroleum Gas) primarily contains propane and butane. The calorific value of LPG is approximately 88-94 MJ/m³, with 94 MJ/m³ being the standard approximate value. This is significantly higher than natural gas (about 38 MJ/m³), making LPG an efficient fuel.