Carbon and Fossil Fuels

Carbon dioxide is the best fire extinguisher among these options because it's heavier than air, forms a blanket that displaces oxygen, and doesn't conduct electricity (safe for electrical fires). Water can spread grease fires and conducts electricity. Woollen cloth can smother small fires but is not as effective or versatile as CO2 for general firefighting.

Carbon dioxide (CO2) is heavier than oxygen and air, which allows it to settle and form a blanket over burning material, displacing the oxygen needed for combustion. CO2 does NOT react with oxygen (option A is wrong), and it does NOT raise temperature (option D is wrong). Its effectiveness comes from being denser than oxygen and physically displacing it.

Charcoal does NOT vaporize when burned - it undergoes solid-to-gas combustion where carbon directly reacts with oxygen, producing CO2 without passing through a liquid or vapor phase. Wax, kerosene, and wood all vaporize first (solid/liquid → gas) before burning - the combustion occurs in the gas phase. This is why charcoal leaves ash residue while the others burn away more completely.

Coal combustion produces carbon dioxide (CO₂) from the carbon content, and releases heat and light energy. Hydrogen gas (H₂) is not a direct product of coal burning; the hydrogen in coal combines with oxygen to form water vapor (H₂O), not hydrogen gas.

Combustion can occur in all three states of matter. Solid fuels like wood and coal burn, liquid fuels like petrol and alcohol burn, and gaseous fuels like natural gas and LPG burn. The physical state does not prevent combustion if the ignition temperature is reached.

Inflammable substances have very low ignition temperatures, meaning they can catch fire very easily with minimal heat input. Examples include petrol, alcohol, and LPG. The term 'inflammable' is synonymous with 'highly flammable'.

Wood has a relatively high ignition temperature (around 300°C). A matchstick produces brief, localized heat that is insufficient to raise the wood's temperature to its ignition point before the match extinguishes. Sustained contact or kindling is needed to reach the ignition temperature.

The fire triangle requires three essential components: fuel, oxygen (or an oxidizing agent), and heat. These three must be present for fire to exist. Carbon dioxide is NOT required for fire - in fact, it's used to extinguish fires by displacing oxygen.

Petrol, alcohol, and LPG have very low ignition temperatures and are classified as inflammable (easily ignitable). Wood is combustible but has a relatively high ignition temperature and requires sustained heat to burn. Wood is not considered an inflammable substance in the strict sense.

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

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.

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 .