Carbon and Fossil Fuels

Reactive metals like sodium, magnesium, and potassium react violently with water. Dry chemical powder smothers these Class D fires without causing dangerous reactions.

Dry chemical powder is suitable for electrical fires (Class C) as it doesn't conduct electricity and effectively smothers the fire. CO2 is also used but leaves no residue.

Nylon is a synthetic polymer made from precursors derived from coal, water, and air (petroleum products). Petroleum jelly is a byproduct of petroleum but not coal. Teflon and Crayon have different chemical compositions.

High speed engines operate on the dual combustion cycle, which combines features of both Otto and Diesel cycles. This cycle involves constant volume heat addition followed by constant pressure heat addition, making it suitable for high-speed applications.

By definition, one petroleum barrel equals exactly 42 US gallons - a standard established in the 1860s Pennsylvania oil fields. This measurement is still used globally today for oil trading.

Carbon dioxide (CO2) extinguishes petrol fires by displacing oxygen and smothering the flames. CO2 is heavier than air and forms a blanket over the fuel. Water is ineffective and dangerous for petrol fires because petrol floats on water and can spread the fire. Sand can work by smothering but is less practical and reliable than CO2 extinguishers.

RDX stands for 'Research Department Explosive' or 'Research Developed Explosive'. It's a powerful explosive compound widely used in military applications. The other options are fabricated expansions that don't correspond to the actual abbreviation.

Petrol (gasoline) has an energy density of approximately 45 MJ/kg, making it an efficient fuel for transportation. Option A (10 MJ/kg) is too low, option B (25 MJ/kg) is closer but still low, and option D (120 MJ/kg) is more characteristic of hydrogen or nuclear energy sources.

Option D (NaCl + AgNO3 → NaNO3 + AgCl) is a precipitation/double displacement reaction, not a combustion process. Combustion involves rapid oxidation with heat and light (options A, B, C all show fuel + oxidizer → products). Option C shows reaction with fluorine, which is even more vigorous than typical combustion.

Natural gas is preferred for heating because it burns cleanly, has high energy density, and produces a high-temperature flame. The high flame temperature makes it efficient for heating applications. 'Slow' and 'fast' are not standard descriptors for flame temperature - the quality is high or low temperature.

Naphtha is a flammable liquid hydrocarbon mixture. Because its boiling range and chemical properties are somewhat similar to petrol, it is frequently used as an illegal adulterant in fuel markets.

Anthracite is the correct answer. It is the highest grade coal with 86-97% carbon content, burns hottest with minimal smoke and pollutants, and is considered cleanest. Lignite is lowest grade (25-35% carbon), very polluting. Bituminous is intermediate grade (45-86% carbon) with significant smoke and pollutants.

Natural gas is the cleanest fossil fuel when burned. It produces primarily CO2 and water vapor with minimal pollutants like SO2, particulates, and mercury compared to coal and oil. Its high hydrogen-to-carbon ratio means more energy per unit of carbon emitted.

Crude oil is primarily composed of hydrocarbons (mixtures of hydrogen and carbon molecules) plus impurities like sulfur, nitrogen, oxygen compounds, and metals. The hydrocarbons range from light gases to heavy tars, which refineries separate into different products.