Tag: science & technology

Diamond is the hardest known naturally occurring substance on Earth, ranking 10 on the Mohs scale of mineral hardness. Its exceptional hardness comes from the strong covalent bonds between carbon atoms in its crystal structure.

Peat is the lowest grade of coal and contains recognizable traces of the original plant material from which it formed. It's the first stage in coal formation, followed by lignite, bituminous coal, and anthracite in increasing maturity.

Tetraethyl lead (TEL) was historically used as an additive in petrol (gasoline) to improve octane rating and prevent engine knocking. It's an organolead compound that was phased out due to environmental and health concerns.

Graphite is an excellent solid lubricant due to its layered structure. The weak van der Waals forces between graphene layers allow them to slide easily over each other, making graphite useful in locks, hinges, and industrial applications.

Deep sea divers breathing compressed air can experience nitrogen narcosis. Helium is substituted for nitrogen in breathing mixtures because it's inert and doesn't cause narcosis, allowing divers to work at greater depths safely.

Oxy-acetylene welding is the most common gas welding process, using oxygen and acetylene to produce a very hot flame (around 3,200°C). Other gases like argon are used in TIG/MIG welding but not as commonly in traditional gas welding. The combination of oxygen and acetylene is the standard answer for general welding gas questions.

Deliquescence occurs when a hygroscopic substance absorbs moisture from air and dissolves in it (e.g., sodium hydroxide pellets). Efflorescence is the opposite - losing water to become powdery. Osmosis involves solvent movement through membranes. Desiccation actively removes moisture.

Silicon carbide is an extremely hard material (9-9.5 on Mohs scale) used as an abrasive and in cutting tools for hard substances. It is not used in cement/glass production, water disinfection (that's chlorine), or statue casting (that's plaster/metal).

The average salinity of seawater is 3.5% (35 parts per thousand). This is a standard oceanographic fact. Salinity varies slightly by region (higher in enclosed seas, lower near river mouths), but 3.5% is the accepted global average.

Rusting is the oxidation of iron where iron reacts with oxygen from air to form iron oxide (Fe2O3). During this process, oxygen atoms combine with iron, so the total mass of the nail increases. The weight does not stay the same (A and D are wrong) nor does it decrease (B is wrong).