General Science Questions and Answers

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

Deliquescence is the property of absorbing so much moisture from the air that the substance dissolves in it, forming a solution.

Calcium chloride and sodium hydroxide are deliquescent. The opposite is efflorescence, where a hydrated crystal loses its water to the air and crumbles to powder.

Answer: B

The main constituent of biogas is methane, usually 50 to 70 per cent, the rest being mostly carbon dioxide.

It is produced by anaerobic bacteria digesting cattle dung and other organic waste, and the slurry left behind is a good manure. Biogas plants are widely used in rural India.

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: B

The cell membrane is selectively permeable. It lets water and small non-polar molecules through freely, but admits ions, sugars and amino acids only through specific channels and pumps.

This selectivity is what allows a cell to keep its internal composition quite different from its surroundings. A semipermeable membrane, by contrast, sorts only by size.

Answer: A

Poor hygiene is the biggest cause of foodborne illness - unwashed hands above all, which transfer bacteria and viruses from a food handler to the food.

The other listed items are ways it happens rather than the underlying cause. Handwashing, temperature control and avoiding cross-contamination prevent most cases.

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: B

The north pole of a magnet attracts a piece of iron that is not itself a permanent magnet. The field induces magnetism in the iron, with the near face becoming a south pole, so the two attract.

Two north poles repel each other, and a charged rod carries an electric charge, not a magnetic pole, so a stationary magnet exerts no force on it.

Answer: D

Sulphuric acid is H₂SO₄ - two hydrogen atoms, one sulphur and four oxygen.

It is a dibasic strong acid and the most produced industrial chemical in the world, used in fertilisers, refining, dyes and batteries. K₂SO₄ and Na₂SO₄ are its salts and SO₂ is an oxide of sulphur.

Answer: C

Nichrome - an alloy of about 80 per cent nickel and 20 per cent chromium - is used for the heating elements of electric heaters, irons and toasters.

It has high resistivity, so it heats strongly for a modest current, and it does not oxidise away at red heat because the chromium forms a protective oxide skin.