Tag: science & technology

Options A (H2O2 decomposition) and B (SO2Cl2 decomposition) are classic first-order reactions. Option D (2NO2 decomposition) is second-order because rate depends on [NO2]². Option C uses an incorrect formula (N2O2 is not stable; should be N2O5 for first-order decomposition), making it the 'not first-order reaction' by being chemically invalid.

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.

The flame velocity of a methane-air mixture is approximately 40 cm/s. This is a characteristic property of methane combustion in air at standard conditions. Option A (10 cm/s) is too slow, while options C and D (1 m/s and 4 m/s) are an order of magnitude too fast.

A typical candle releases energy at approximately 15 W. This represents the heat output from the combustion of wax. Options B, C, and D (45 W, 75 W, 150 W) are too high for a small candle flame.

A typical matchstick requires approximately 0.004 J (4 millijoules) of energy to ignite. This is the activation energy needed to initiate the combustion reaction of the match head. Options A, B, and C (0.4 J, 4 J, 0.04 J) are all too high for a match ignition.

The lower flammability limit (LFL) of hydrogen in air is 4% by volume. Below this concentration, the mixture is too lean to burn. Options A (0.4%), B (3%), and D (8%) are incorrect - 0.4% is too low, 3% is close but not the standard value, and 8% approaches the upper flammability limit.

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.

An oxy-acetylene torch typically achieves temperatures around 3000°C. This is due to the complete combustion of acetylene in pure oxygen. Options A (1000°C) and B (2000°C) are too low, while option D (5000°C) exceeds the theoretical flame temperature of acetylene-oxygen combustion.

A spark in a car engine typically releases energy for approximately 2 milliseconds. This brief duration is sufficient to ignite the fuel-air mixture. Options B (0.5 ms) is too short, while options C (10 ms) and D (25 ms) are too long for an efficient spark discharge.