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: B

Raindrops are spherical because of surface tension. The molecules at a liquid's surface are pulled inward by their neighbours, so the drop takes the shape with the least surface area for its volume - a sphere.

Large drops are in fact flattened by air resistance as they fall, and only small ones stay truly spherical.

Answer: A

The nautical mile is used in navigation at sea and in the air. It equals 1,852 m, defined as one minute of arc of latitude along a meridian.

That definition is what makes it useful: a degree of latitude is 60 nautical miles, so distance can be read straight off a chart's latitude scale.

Answer: D

Ampicillin is an antibiotic, a semi-synthetic penicillin effective against a broader range of bacteria than penicillin itself.

Like all penicillins it works by preventing bacteria from building their cell walls, so it kills only growing cells and has no effect on viruses.

Answer: A

The seasons are caused by the tilt of the earth's axis, about 23½° to the plane of its orbit, which stays pointed in the same direction as the earth goes round the sun.

Each hemisphere therefore leans towards the sun for half the year and away for the other half, changing both the angle of the sun's rays and the length of the day. Distance from the sun has nothing to do with it - the earth is in fact closest in January.

Answer: C

Dengue fever is not spread by the housefly. It is transmitted by the bite of the Aedes aegypti mosquito.

The housefly carries disease mechanically, on its feet and mouthparts, from filth to food - which is how it spreads cholera, dysentery, typhoid and diarrhoea.

Answer: C

Gamma rays are the most penetrating of the radiations listed. They are high-energy electromagnetic waves with no charge and no mass, and need several centimetres of lead or a metre of concrete to stop them.

Alpha particles are stopped by a sheet of paper and beta particles by a few millimetres of aluminium. X-rays are of the same nature as gamma rays but of lower energy.

Answer: A

Jonas Salk developed the first effective polio vaccine, announced in 1955. It used killed virus and was given by injection.

Albert Sabin's live oral vaccine followed a few years later and, being cheaper and easier to give, became the mainstay of mass campaigns. Salk refused to patent his vaccine.

Answer: A

Under Avogadro's hypothesis, the smallest particle of an element or compound that can exist independently is the molecule.

An atom of most elements cannot exist alone - oxygen occurs as O₂, nitrogen as N₂. Cations and anions are charged particles and are always found paired with an opposite charge.

Answer: B

Carbon dioxide from fossil fuels is the main cause of the rise in average global temperature. Burning coal, oil and gas has raised its atmospheric concentration from about 280 ppm before the industrial era to over 420 ppm today.

Ozone depletion is a separate problem: it admits more ultraviolet radiation but does not by itself warm the lower atmosphere.