General Science Questions and Answers

Answer: D

Among carbon's allotropes, diamond is the hardest and graphite the softest.

The difference is structural: in diamond every atom is bonded to four others in a rigid three-dimensional network, while graphite is built of flat sheets held together only by weak forces, so the sheets slide over one another. That is why graphite works as a lubricant and as pencil lead.

Answer: D

Gun metal is an alloy of copper, tin and zinc - typically 88:10:2.

It was used for cannon because it is strong, easily cast and resists corrosion; it is now used for steam and hydraulic fittings for the same reasons.

Answer: A

Alloys are harder than the pure metal they are based on. Atoms of a different size disturb the regular lattice, so the layers cannot slide over one another as easily.

That is why gold is alloyed with copper for jewellery and iron with carbon for steel - the pure metals are too soft to be useful.

Answer: D

Lead is the metal used in storage batteries. A car battery has plates of lead and lead dioxide in sulphuric acid.

Discharging converts both plates to lead sulphate; charging reverses it. The reaction is efficiently reversible and delivers very high current, which is what a starter motor needs.

Answer: B

Filtration does not kill micro-organisms. It removes suspended matter and, with a fine enough filter, most bacteria and protozoan cysts, but whatever passes through is still alive.

Boiling, chlorination and ultraviolet irradiation all destroy the organisms rather than merely removing them.

Answer: B

Bromine is the non-metal that is liquid at room temperature - a dense, dark red-brown liquid giving off a choking red vapour.

It is the only liquid non-metal; mercury is the only liquid metal. Chlorine is a gas, phosphorus a solid, and helium a gas.

Answer: A

The PSLV was developed and is operated entirely indigenously in India, by ISRO.

First flown in 1993, it has become the workhorse of the Indian programme, launching Chandrayaan-1, the Mars Orbiter Mission and, in a single flight in 2017, a record 104 satellites.

Answer: B

CFCs were used in refrigerators and air conditioners as the working refrigerant, and also as aerosol propellants and foam-blowing agents.

They are being phased out under the Montreal Protocol because chlorine released from them in the stratosphere destroys ozone - one chlorine atom can break down thousands of ozone molecules.

Answer: D

Carbon monoxide is the most dangerous of these pollutants. It is colourless and odourless and binds to haemoglobin about 240 times more strongly than oxygen does.

The blood is then unable to carry oxygen, and a few hundred parts per million can kill within hours without any warning to the victim.

Answer: A

Bauxite is the chief ore of aluminium, a mixture of hydrated aluminium oxides.

The oxide is extracted from it by the Bayer process and then reduced to the metal by electrolysis in molten cryolite. Calamine is a zinc ore, calcite calcium carbonate, and galena lead sulphide.