GK (Science)

Silicon is the most abundant element in the Earth's crust, making up about 28% of its mass. It's primarily found in silicate minerals which are the main constituents of rocks. While oxygen is the most abundant element overall by mass, silicon dominates the rock and mineral composition specifically.

Bauxite is the principal ore of aluminium, containing hydrated aluminium oxides like gibbsite, boehmite, and diaspore. It's the primary commercial source for aluminium extraction through the Bayer process. Bauxite forms through the weathering of aluminium-rich rocks in tropical climates.

Lithium is the lightest metal with an atomic mass of 6.94 and density of 0.534 g/cm³. It's so light that it floats on water and is the first element in the alkali metal group. This property makes it invaluable for lightweight batteries and aerospace applications where weight reduction is critical.

German Silver is actually a copper-nickel-zinc alloy despite its name containing no silver. It's called 'German Silver' or 'Nickel Silver' because of its silver-like appearance. This alloy is corrosion-resistant and used for coins, musical instruments, and silverware as an economical alternative to actual silver.

Nichrome is a nickel-chromium alloy specifically designed for heating elements due to its high electrical resistance and ability to withstand extreme temperatures without oxidizing. It maintains structural integrity even when red-hot, making it ideal for electric heaters, toasters, and hair dryers. The resistance generates heat while the material itself remains stable.

Air is a mixture of gases, primarily nitrogen (78%), oxygen (21%), and trace gases like argon, carbon dioxide, and water vapor. A mixture can be separated by physical means, unlike a compound which has fixed chemical bonding. The composition of air varies slightly with location and altitude, confirming it's a mixture rather than a compound.

Sea water is the best conductor because it contains dissolved salts like sodium chloride which ionize and create free-moving charged particles. These ions carry electrical current much more effectively than pure water. Ordinary water has some dissolved ions but far fewer than sea water, while distilled and boiled water have almost no ions.

Helium is used to fill balloons because it's lighter than air and non-flammable, unlike hydrogen which is also light but extremely dangerous. Helium is a noble gas that doesn't react with other substances. Being the second lightest element after hydrogen, it provides the lift needed for balloons and airships while remaining completely safe.

Aluminium is the most abundant metal in Earth's crust at about 8% by mass, though it's never found free in nature. It's always combined with oxygen and other elements in compounds like bauxite. While iron is more abundant in the entire Earth (including the core), aluminium dominates the crust specifically where we can access it.

Wood charcoal is used to decolorize raw sugar through the process of adsorption where impurities stick to the porous charcoal surface. The activated carbon in wood charcoal has a massive surface area that traps colored compounds. This process filters out the brown color from raw sugar juice, producing the white refined sugar we commonly use.

Gobar gas is produced by anaerobic digestion of organic matter like cow dung. The main component is methane (CH4), typically 50-70%, making it a combustible fuel gas. Carbon dioxide is also present but as a secondary component.

All acids contain hydrogen ions (H+). When acids dissolve in water, they release H+ ions, which is why hydrogen is the defining element present in all acidic compounds. Oxygen is not present in all acids (e.g., HCl).

Radium was first isolated from pitchblende (also called uraninite) by Marie and Pierre Curie in 1898. Pitchblende is a uranium-rich ore that contains trace amounts of radium along with other radioactive elements. The Curies processed tons of pitchblende to extract small amounts of radium.

Diamond is used for protective windows in space probes because of its exceptional hardness, thermal conductivity, and transparency to a wide range of electromagnetic radiation. Diamond can withstand extreme conditions, micrometeoroid impacts, and radiation while maintaining optical clarity.

Nitrous oxide (N2O) is commonly called laughing gas because it inhalation produces euphoria and laughter. It was discovered by Joseph Priestley and has been used as an anesthetic and analgesic in dentistry and surgery for over 150 years.

Red phosphorus is used in safety matches because it is stable and less reactive than white phosphorus. The striking surface contains red phosphorus, which reacts with the match head compounds when rubbed against it. White phosphorus is too dangerous and spontaneously ignites in air.

Stainless steel is primarily an alloy of iron, chromium (10-30%), and nickel. Chromium provides corrosion resistance by forming a passive oxide layer, while nickel enhances strength and corrosion resistance. Carbon is present in small amounts but not a primary alloying element.

Green vitriol is actually ferrous sulphate (FeSO4), not copper sulphate (CuSO4). Copper sulphate is called blue vitriol. The other options are correctly matched: Galena is lead sulphide (PbS), Plaster of Paris is calcium sulphate hemihydrate, and Calomel is mercurous chloride (Hg2Cl2).

Mercury is the only metal that forms amalgams (alloys) with other metals at room temperature. This unique property is because mercury is liquid at room temperature and can dissolve many other metals. Amalgams have various applications, including in dentistry and gold extraction.

Silicon carbide (SiC) is one of the hardest synthetic materials, ranking just below diamond on the Mohs scale. It's extensively used as an abrasive for cutting and polishing very hard substances like glass, ceramics, and other carbides. The other options don't match SiC's primary applications.

Gold is the most malleable metal, meaning it can be hammered into extremely thin sheets without breaking. A single gram of gold can be beaten into a sheet covering several square meters. Silver and aluminum are also malleable but not to the same extent as gold, while sodium is too reactive.

Bromine is the only non-metal that exists as a liquid at room temperature (25°C). It's a dense, reddish-brown liquid that evaporates easily to form a red vapor. Chlorine is a gas, helium is a noble gas, and phosphorus is a solid (white phosphorus is waxy, red phosphorus is powdery).

Tetraethyl lead (TEL) was historically added to petrol as an anti-knocking agent to improve engine performance by preventing premature fuel combustion. It works by increasing the octane rating of gasoline, allowing for smoother engine operation. The other options are incorrect because TEL is not used as a mosquito repellent, pain killer, or fire extinguisher.

Sulphur compounds have been traditionally used in hair setting treatments because they can help break and reform disulfide bonds in hair proteins, allowing for permanent styling. The other options are incorrect - phosphorus is a fertilizer element, chlorine is a disinfectant, and silicon is used in electronics and cosmetics as a different type of treatment.

Carbon dioxide is the primary gas used in fire extinguishers because it displaces oxygen and does not support combustion, effectively smothering fires. It's particularly useful for electrical fires as it's non-conductive. Carbon monoxide is toxic and would be dangerous, while neon and nitrogen are not effective fire suppressants in standard applications.