General Science Questions and Answers

Answer: D

The rule that no two electrons in an atom may share all four quantum numbers is Pauli's exclusion principle.

It is why each orbital holds at most two electrons, of opposite spin, and it is what gives the periodic table its structure. The Aufbau principle is different: it says orbitals fill in order of increasing energy.

Answer: A

The stratosphere is very dry. Almost no water vapour reaches it, because air rising through the tropopause is chilled to about −60°C and its moisture freezes out first.

The layer is also very stable, with temperature rising with height, so there is little vertical mixing to carry moisture up. This is why jet aircraft cruise there in cloudless air.

Answer: A

PVC is made by polymerising vinyl chloride, CH₂=CHCl.

The molecules add end to end into long chains. PVC is rigid on its own and is used for pipes and window frames; adding a plasticiser makes it flexible for cable insulation and sheeting.

Answer: D

The alcohol thermometer reads the lowest temperatures. Alcohol freezes at about −115°C, so it stays liquid far below mercury, which freezes at −39°C.

This is why alcohol thermometers are used in polar and high-altitude conditions, usually with the alcohol dyed red to make it visible.

Answer: A

Nuclear fission is triggered by the impact of a neutron.

Being uncharged, a neutron is not repelled by the nucleus and can reach it at low energy. Each fission releases two or three more neutrons, which is what makes a chain reaction possible.

Answer: D

Dermatology is the branch of medicine dealing with the skin, from the Greek derma.

It also covers hair and nails. The skin is the body's largest organ, about 1.7 square metres and a sixth of body weight in an adult.

Answer: A

Eugenics is the study of ways to improve or impair the inherited qualities of future generations, physically or mentally, by controlling who reproduces.

Galton coined the term in 1883. In the twentieth century it was used to justify forced sterilisation and worse, and it is now wholly discredited as a programme.

Answer: C

Urea is removed from the blood by the kidneys.

It is made in the liver from the ammonia produced by breaking down surplus amino acids, carried in the blood to the kidneys, filtered out at the glomerulus and excreted in urine. A healthy adult passes about 25 to 30 g of it a day.

Answer: A

Light is far faster than sound - 3 × 10⁸ m/s in vacuum against about 340 m/s for sound in air, roughly 900,000 times faster.

This is why lightning is seen before the thunder is heard, and why counting the seconds between them gives the distance of the storm at about 3 seconds per kilometre.

Answer: B

A metal that can be drawn out into wire is ductile. Gold is the most ductile of all - a single gram can be drawn into a wire two kilometres long.

A metal that can be hammered into thin sheets is malleable instead. Most metals are both, because their layers of atoms can slide over one another without the bonding breaking.