General Science GK Questions with Answers – Page 108

The prefix di stands for two and the ending ene for a carbon to carbon double bond, so a diene is a hydrocarbon carrying exactly two such bonds; buta-1,3-diene, the raw material of synthetic rubber, is the standard example.

Hexane, C6H14, can be drawn as a straight chain of six carbons, as two chains of five carbons with a methyl branch in different positions, and as two chains of four carbons carrying branches, which gives five different structures with the same molecular formula.

Liquefied petroleum gas is a mixture of these two saturated hydrocarbons, which are gases at ordinary pressure but turn liquid under moderate pressure, so a large quantity of fuel fits into a small cylinder; a strong-smelling compound is added so that a leak is noticed.

Graphite is an allotrope of carbon in which each atom is bonded to three others, leaving one electron per atom free to move through the layers, so it conducts electricity although it is a non-metal; this is why graphite is used for electrodes and in dry cells.

An amphoteric oxide reacts with both acids and bases to form salts, and aluminium oxide does exactly that, behaving as a base towards hydrochloric acid and as an acid towards sodium hydroxide; zinc oxide is the other amphoteric oxide asked in examinations.

In galvanisation iron or steel is given a coating of zinc, usually by dipping it in the molten metal, and the coating protects the iron in two ways: it keeps out air and moisture, and because zinc is more reactive than iron it corrodes in place of the iron even…

Galena is lead sulphide, the principal ore from which lead is obtained; being a sulphide it is concentrated by froth flotation and then roasted in air to the oxide before reduction.

Silver has the highest electrical conductivity of all metals and also the highest thermal conductivity, but it is costly and tarnishes, so it is used only in specialised contacts and instruments.

Aqua regia is three parts concentrated hydrochloric acid to one part concentrated nitric acid, and the name means royal water, given because the mixture attacks the noble metals gold and platinum, which neither acid can dissolve on its own.

Mercury is the only metal that is liquid at ordinary room temperature, which is why it was long used in thermometers and barometers; it is also the metal that forms amalgams, alloys in which mercury is one component.

Brass takes the workability of copper and the hardness of zinc, resists corrosion and is easy to cast, which is why it is used for utensils, locks, taps, fittings and wind instruments.

Ductility is the property of being drawn into a wire, and gold is the most ductile metal known; it is also the most malleable, so a very small quantity can be beaten into an extremely thin sheet or drawn into a very long wire.

Silver is an element, a pure metal with its own place in the periodic table, so it cannot be an alloy; an alloy is a homogeneous mixture of two or more metals, or of a metal with a non-metal such as carbon.

Calamine is zinc carbonate, and since it is a carbonate ore it is converted to the oxide by calcination, that is by heating in the absence of air, before being reduced to the metal.

The female egg cell, or ovum, is the largest cell in the human body. It measures about 100 to 130 micrometres across, roughly the thickness of a hair, and is the only human cell that can just be seen without a microscope.

The poise is the CGS unit of dynamic or absolute viscosity, named after the French physician Jean Poiseuille, and one poise equals one dyne-second per square centimetre, which is the same as one gram per centimetre per second.

Geitonogamy is pollination between two different flowers borne on the same plant.

The buccal cavity is the mouth, and the saliva poured into it begins the digestion of starch, a carbohydrate. Three pairs of salivary glands supply saliva, which carries the enzyme salivary amylase, also called ptyalin.

All three are unicellular, which means a single cell carries out every job of life. In a unicellular organism that one cell manages nutrition, respiration, movement and reproduction, while a multicellular body shares the work among tissues and organs.

The grooves cut into a sole grip the ground, so the foot does not slip while walking or running. Friction is the force that acts between two surfaces in contact and opposes motion between them.