General Science GK Questions with Answers – Page 89

Its calorific value is about 150 kilojoules per gram, the highest of any known fuel, roughly three times that of petrol, and its only combustion product is water vapour, which makes it a clean fuel as well.

In this zone the supply of air is unrestricted, so combustion is complete and all the carbon of the fuel is converted to carbon dioxide, releasing the maximum heat.

Calorific value is the heat released on completely burning one gram of a substance, and among the four foods listed ghee has the highest, because it is almost entirely fat.

In spontaneous combustion a substance catches fire by itself, without any external flame being brought near it.

Nichrome is an alloy of nickel, chromium and iron with a high electrical resistance and a high melting point, and it does not oxidise easily when red hot, so a nichrome wire can glow for years without burning away; that combination makes it the standard material for the heating elements…

Limestone decomposes in the furnace to calcium oxide, a basic flux, which combines with the acidic silica gangue of the ore to form calcium silicate, a fusible slag that floats on the molten iron and is drawn off separately.

In the Mond process impure nickel is heated in a stream of carbon monoxide at a moderate temperature, forming the volatile compound nickel tetracarbonyl; the vapour is led away from the solid impurities and heated more strongly, whereupon it decomposes and deposits very pure nickel.

Galvanisation is the coating of iron or steel with zinc, usually by dipping it in molten zinc.

Pure alumina melts at a very high temperature, so in the Hall and Heroult process it is dissolved in molten cryolite, sodium hexafluoroaluminate, usually with some fluorspar, which lowers the working temperature of the bath and makes the melt a far better conductor of electricity.

German silver is an alloy of copper, zinc and nickel, and its name comes from its white silvery appearance, not from its composition, since it contains no silver at all; it is used for tableware, ornaments and electrical contacts.

Brass is made by alloying copper with zinc, which gives a metal harder than copper, easier to cast and machine, and resistant to ordinary corrosion, so it is used for utensils, taps and fittings and the bodies of musical instruments.

Zone refining rests on the fact that impurities are more soluble in a molten metal than in the same metal when solid.

Calcination is the heating of an ore in the absence or a limited supply of air and below its melting point, so that water of hydration and carbon dioxide are driven off; it is therefore the step used for carbonate ores such as calamine and for hydrated ores such as…

In froth flotation the powdered ore is agitated with water, a frothing agent such as pine oil and a collector.

Galena is lead sulphide, with the formula PbS, and is the principal ore from which lead is extracted; being a sulphide, it is concentrated by froth flotation and then roasted to the oxide before reduction.

Malleability is the property of being beaten into thin sheets and ductility the property of being drawn into wires, and gold possesses both to the highest degree of any metal: a single gram can be beaten into a sheet of about one square metre and drawn into a wire of…

A cell whose nucleus is well organised and bounded by a nuclear membrane is called a eukaryotic cell. The word comes from the Greek eu, meaning true, and karyon, meaning kernel or nucleus.

Atomic number 59 is praseodymium, a lanthanide, and the lanthanides and actinides together make up the f-block. A block is named after the sub-shell that the last electron enters.

Concrete is the building material made by mixing cement with coarse aggregate such as gravel, fine aggregate such as sand, and water.

Aluminium is the most abundant metal in the crust of the earth, making up about eight per cent of it by weight.