General Science Questions and Answers

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: A

Ethyl mercaptan (ethanethiol, C₂H₅SH) is a compound of sulphur, added to LPG to give it a smell.

LPG is odourless, so a leak would otherwise go unnoticed until it reached an explosive concentration. The human nose detects mercaptan at a few parts per billion.

Answer: D

Magnesium is the metal at the centre of the chlorophyll molecule, the green pigment of the leaf.

Each chlorophyll molecule holds a single magnesium atom in a porphyrin ring, and it is this arrangement that absorbs red and blue light and reflects green. A magnesium-deficient plant turns yellow between the veins.

Answer: C

Detergents contain sulphonates - usually the sodium salts of long-chain alkyl benzene sulphonic acids.

The sulphonate head does the job the carboxylate head does in soap, but its calcium and magnesium salts are soluble, so a detergent lathers in hard water where soap forms a scum.

Answer: B

Foot-and-mouth disease affects cattle and pigs, along with sheep, goats and other cloven-hoofed animals.

It is a highly contagious viral disease that causes blisters in the mouth and on the feet. It rarely kills adult animals but destroys their productivity, so outbreaks are met with slaughter and movement restrictions.

Answer: C

A thermometer is graduated in degrees as a clock is graduated in hours - in each case the second word names the unit the instrument measures in.

Wall, tower and cock are merely things associated with clocks, not the unit they read.

Answer: A

Washing soda is hydrated sodium carbonate, Na₂CO₃·10H₂O.

It softens water by precipitating the calcium and magnesium as carbonates, so soap can lather. Baking soda is a different compound, sodium bicarbonate.

Answer: D

All three - vitamin C, niacin and riboflavin - are water-soluble.

The water-soluble vitamins are C and the B group. They are not stored in the body to any extent, so a surplus is excreted in urine and a regular supply is needed. Vitamins A, D, E and K are fat-soluble and are stored in the liver.

Answer: B

Rhyolite caldera complexes are the most explosive volcanoes of all.

Their magma is silica-rich, so it is extremely viscous and traps gas until the pressure blows the whole chamber apart and its roof collapses into a caldera. Yellowstone and Toba are examples; a single eruption can eject thousands of cubic kilometres.

Answer: A

The macronutrients - fat, carbohydrate and protein - are listed at the top of a nutrition label, immediately under the serving size and calories.

Vitamins and minerals, the micronutrients, follow lower down. The order reflects the quantities in which the body needs them.