Chemistry of Metals and Alloys

Diamond, a form of carbon, is the hardest known substance.

Yes, all have no unpaired electrons, hence all are colourless.

Bronze is made up of alloys of coppers and tin

Lithium is the lightest metal with an atomic number of 3 and atomic weight of approximately 6.94. It's an alkali metal that floats on water and is less dense than any other metal. The other options are incorrect: chromium is a transition metal, bromine is a liquid nonmetal (not a metal at all), and zinc is a transition metal - all are significantly heavier than lithium.

Mercury is the only metal that is liquid at room temperature. Bromine is also liquid at room temperature, but it is a non-metal (halogen), not a metal. Hydrogen is a gas, and aluminum is a solid metal.

Bell metal is an alloy and consists of Cu = 80%, Sn = 20%. Wood metal consists of Bi = 50%, Pb = 25%, Sn = 12.5% & Cd = 12.5% and is used in the making of automatic sprinklers as it melts in hot water (m.p.= 68 ^oC). Duralumin is used in the manufacturing of aeroplane parts and consists of Al = 95.5%, Cu = 4%, Mg = 0.5% and Mn = 0.5%.

Silicon is a semiconductor material and is used in chip manufacturing.

Nichrome is a non-magnetic alloy of nickel, chromium, and often iron, usually used as a resistance wire . Due to its relatively high electrical resistivity and resistance to oxidation at high temperatures, it is widely used in electric heating elements, such as in hair dryers, electric ovens, soldering iron, toasters, and even electronic cigarettes.

Elektron is a magnesium alloy. It is unusually light and has a specific gravity of about 1.8 compared with  2.8 of aluminium alloy.The alloy variants are used in auto racing and aerospace engineering applications due to magnesium's relatively low density.

Electrum is a naturally occurring alloy of gold and silver, with trace amounts of copper and other metals. Electrum was used as early as the third millennium BC in Old Kingdom of Egypt, sometimes as an exterior coating to the pyramidions atop ancient Egyptian pyramids and obelisks.

Mischmetal is an alloy of rare earth elements in various naturally-occurring proportions. A typical composition includes approximately 50% cerium and 25% lanthanum, with small amounts of neodymium and praseodymium. Its most common use is in the flint ignition device of many lighters and torches.

Megallium is an alloy of 60% cobalt, 20% chromium, 5% molybdenum, and traces of other substances. It is used in dentistry because of its light weight, resistance to corrosion and hypo-allergenic (nickel free) properties.

Stainless steel requires at least 10.5% chromium, which forms a protective oxide layer on the surface that prevents rust and corrosion. This chromium oxide layer is self-repairing when scratched in the presence of oxygen.

Numismatic evidence confirms that Satavahana coins were minted in copper, lead, potin (a copper alloy), and silver. Gold was not a standard metal for their coinage, eliminating options A and D. Option C matches the historical record.

German silver, also known as nickel silver, is an alloy composed of copper, nickel, and zinc - it contains NO actual silver despite its name. The name comes from its silver-like appearance. Silver (option C) is indeed not present in German silver, which is why this answer is correct.