General Science Questions and Answers

Answer: C

One fathom is 1.8288 m, exactly 6 feet.

\[ 6 \times 0.3048 = 1.8288\ \mathrm{m} \]

The unit is used for the depth of water and comes from the Old English for the span of a man's outstretched arms.

Answer: C

Nitrous oxide (N₂O) is the oxide of nitrogen used as an anaesthetic. Known as laughing gas, it has been used in dentistry and surgery since the 1840s.

Nitric oxide and nitrogen dioxide are toxic, and nitrogen pentoxide is an unstable solid that reacts violently with water - none of them could be breathed.

Answer: C

The kangaroo rat of the North American deserts never drinks. It gets all the water it needs from the metabolic breakdown of the dry seeds it eats.

It survives by losing almost none: it has no sweat glands, produces extremely concentrated urine and nearly dry droppings, and recovers moisture from its own breath in its nasal passages.

Answer: D

Rust stains are removed with oxalic acid.

It reduces the insoluble iron(III) of the rust and forms a soluble complex with it, so the stain washes out of the fabric. Lemon juice and salt work more slowly by the same principle.

Answer: A

Heavy water is deuterium oxide, D₂O, in which both hydrogen atoms are the heavier isotope with a proton and a neutron.

It occurs naturally as about one part in 6,400 of ordinary water and is about 11 per cent denser. Because it absorbs very few neutrons it is used as a moderator in nuclear reactors, including India's PHWRs.

Answer: B

Curd is sour because of lactic acid.

Lactobacillus ferments the milk sugar lactose into lactic acid, which lowers the pH and coagulates the milk protein casein - so the same acid both sours the milk and sets it.

Answer: C

Atomic number is represented by the letter Z, from the German Zahl, number.

It is the number of protons in the nucleus, and it is what identifies an element. Mass number, the total of protons and neutrons, is written A.

Answer: D

Sugar is the most soluble of these in water - about 200 g dissolve in 100 ml at room temperature, far more than common salt's 36 g.

Sucrose is so soluble because its many hydroxyl groups hydrogen-bond to water. Camphor and sulphur are non-polar and essentially insoluble.

Answer: A

Carbon dioxide is the gas chiefly responsible for global warming. It is not the most powerful greenhouse gas per molecule, but it is released in by far the greatest quantity and persists in the atmosphere for centuries.

Carbon monoxide and nitrogen peroxide are pollutants rather than significant greenhouse gases; nitrous oxide is a greenhouse gas but is present in far smaller amounts.

Answer: A

A red blood cell lives about 120 days. Having no nucleus it cannot repair itself, and it is eventually broken down in the spleen and liver.

The bone marrow replaces about two million of them every second to keep the count steady.