General Science Questions and Answers

Answer: D

Combustion produces both heat and light. It is the rapid reaction of a substance with oxygen, releasing energy fast enough for the gases to glow.

Rusting is also an oxidation but is far too slow to produce a flame, so it gives out heat without light.

Answer: B

The adrenal glands control blood pressure. The cortex secretes aldosterone, which makes the kidney retain sodium and water and so raises blood volume, and the medulla secretes adrenaline, which constricts vessels and speeds the heart.

The thyroid and parathyroid regulate metabolism and calcium instead, and the thymus is part of the immune system.

Answer: C

A mole is the amount of substance containing as many particles as there are atoms in 12 grams of carbon-12.

That number is Avogadro's constant, 6.022 × 10²³. Since 2019 the mole has been defined by fixing that number exactly, rather than by reference to carbon.

Answer: C

The actinides are the fourteen-plus elements from atomic number 89 to 103 - actinium through lawrencium.

They fill the 5f subshell, all are radioactive, and only thorium and uranium occur in any quantity in nature; the rest are made artificially.

Answer: D

85 decibels is the level beyond which prolonged exposure damages hearing, and is the usual occupational safety limit.

Because the scale is logarithmic, the safe exposure time halves for every 3 dB above it. The threshold of pain is far higher, around 120 to 130 dB.

Answer: A

Three-dimensional photographs made with laser light are holograms.

A hologram records the interference pattern between light reflected from the object and a reference beam, so it stores the phase of the light as well as its intensity. Illuminating the record reconstructs the wavefront, and the image shifts as the viewer moves, as a real object would.

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: 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: D

The rain shadow belongs to orographic rainfall.

Moist air forced up a mountain range cools and drops its water on the windward slope; the air descending the far side is already dry and warms further by compression, so the leeward side receives very little rain. The Deccan plateau lies in the rain shadow of the Western Ghats.

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.