General Science Questions and Answers

Answer: D

Sugar is the most soluble of these in water - about 200 g dissolve in 100 ml at room temperature, far more than common salt's 36 g.

Sucrose is so soluble because its many hydroxyl groups hydrogen-bond to water. Camphor and sulphur are non-polar and essentially insoluble.

Answer: C

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

In diamond every atom is bonded to four others in a rigid three-dimensional network; 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 a pencil lead.

Answer: A

Iron, cobalt and nickel are transition metals - elements with a partly filled d subshell.

That configuration gives them their characteristic properties: variable valency, coloured compounds, catalytic activity and, in these three uniquely, ferromagnetism.

Answer: D

LPG consists mainly of propane and butane, with some methane in the mixture.

These gases liquefy under modest pressure at ordinary temperature, so a great deal of fuel is stored in a small cylinder. Ethyl mercaptan is added to give the odourless mixture a warning smell.

Answer: B

An amalgam is an alloy that contains mercury as one of its constituents.

Mercury dissolves most metals at room temperature; the resulting paste can be worked and then hardens as the mercury combines. Dental amalgam is mercury with silver, tin and copper.

Answer: D

Sodium is stored under kerosene. It reacts violently with water and even with the moisture in air, so it must be kept away from both.

Kerosene works because it is a hydrocarbon that does not react with sodium and is dense enough to keep the metal covered. Sodium in air quickly forms an oxide crust and can catch fire.

Answer: D

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.

Answer: D

Air is a mixture, not a compound. Its constituents are not combined in any fixed proportion and retain their own properties.

It is about 78 per cent nitrogen, 21 per cent oxygen and 0.93 per cent argon, with carbon dioxide, water vapour and traces of other gases. Each can be separated by physical means, by fractional distillation of liquid air.

Answer: A

Permanent hardness is removed by adding washing soda, sodium carbonate.

It precipitates the calcium and magnesium as insoluble carbonates:

\[ \mathrm{CaSO_4 + Na_2CO_3 \rightarrow CaCO_3 \downarrow + Na_2SO_4} \]

Boiling removes only temporary hardness, which is due to bicarbonates.

Answer: B

The kilowatt measures power - the rate of doing work, one thousand joules per second.

Energy is measured in joules, or in the kilowatt-hour of the electricity bill, which is power multiplied by time.