Tag: science & technology

Potassium nitrate (KNO3, also known as saltpeter) is widely used as a fertilizer because it provides both potassium and nitrogen - two essential nutrients for plant growth. While historically used in gunpowder and some medicines, its primary modern use is in agriculture. It is not used as salt (NaCl), in glass manufacturing, or as a primary pharmaceutical ingredient.

Sodium carbonate (washing soda, Na2CO3) removes permanent hardness by precipitating calcium and magnesium salts as insoluble carbonates. Lime (Ca(OH)2) only removes temporary hardness. Alum is used for water coagulation, not hardness removal, and potassium permanganate is a disinfectant/oxidizing agent.

Soda water is carbonated water created by dissolving carbon dioxide under pressure. The fizz comes from CO2 bubbles being released. While carbonic acid (H2CO3) forms when CO2 dissolves, the primary component added is carbon dioxide gas itself. Sulphuric and nitrous acids are not present in soda water.

Bauxite is the principal ore of aluminium, containing hydrated aluminium oxides. Galena is lead ore, calamine is zinc ore, and calcite is calcium carbonate. Bauxite must be processed through the Bayer process to extract aluminium metal.

Sugar (sucrose) has the highest solubility in water among the options - about 200g/100mL at room temperature. Common salt has moderate solubility (~36g/100mL), sulphur is virtually insoluble, and camphor is only slightly soluble. Sugar molecules form strong hydrogen bonds with water, enabling high solubility.

Helium was first discovered in the solar spectrum in 1868 by Norman Lockyer and Pierre Janssen, who noticed a spectral line (D3 line) that didn't match any known element - 25 years before it was found on Earth. The name means 'sun element'. Krypton, xenon, and neon were discovered later through terrestrial means.

Francium is liquid at or slightly above room temperature (melting point ~27°C), though it's extremely rare and radioactive. Lithium melts at 180°C, sodium at 98°C, and cerium at 795°C - all solid at room temperature (25°C). Francium's low melting point follows the trend of increasing atomic size in Group 1.

Sodium is stored under kerosene because it reacts violently with air and water. Kerosene forms a protective layer, preventing contact with moisture and oxygen. Petrol could work but is more expensive and volatile. Alcohol reacts with sodium, and water causes explosive reactions.

Gun metal (or gunmetal) is a bronze alloy composed of copper (85-90%) and tin (10-15%), known for strength and corrosion resistance - historically used for cannons. It does not contain iron, brass (copper+zinc), or titanium. The incorrect options all include iron, which is not part of traditional gun metal.

Pitchblende (also known as uraninite) is a uranium-rich mineral ore that served as the primary historical source for radium extraction. Marie Curie processed tons of pitchblende to isolate radium. Rutile is a titanium ore, haematite is an iron ore, and limestone is calcium carbonate.