General Science Questions and Answers

Answer: D

An object weighs least at the centre of the earth, where it weighs nothing at all.

There the mass of the earth surrounds it equally in every direction, so the pulls cancel exactly and \( g = 0 \). Weight is greatest at the poles, where the radius is smallest and there is no rotational effect.

Answer: B

The Thumba Equatorial Rocket Launching Station is at Thumba near Thiruvananthapuram, in Kerala.

It was chosen because it lies almost on the magnetic equator, which suits the study of the equatorial electrojet. India's first sounding rocket was launched from it in November 1963.

Answer: A

Uranium-235 is the isotope that sustains a chain reaction. It fissions when it absorbs a slow neutron and releases two or three more, which can go on to split further nuclei.

It makes up only 0.7 per cent of natural uranium; the rest is U-238, which does not fission with slow neutrons. Enrichment raises the U-235 fraction for reactor fuel.

Answer: A

Weight is not an intensive property. It depends on how much material there is, which makes it extensive.

Density, refractive index and melting point are intensive: they are the same for a drop of water as for a lake of it.

Answer: D

An acid reacting with a metal carbonate gives a salt, water and carbon dioxide:

\[ \mathrm{Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2} \]

The effervescence of carbon dioxide is the standard laboratory test for a carbonate; the gas turns limewater milky.

Answer: A

Stress accumulating along the boundaries of lithospheric plates is released as earthquakes. The rocks lock, strain builds, and eventually the fault slips and the stored elastic energy radiates as seismic waves.

This is why the world's earthquake belts trace the plate boundaries almost exactly.

Answer: A

The nautical mile is used in navigation at sea and in the air. It equals 1,852 m, defined as one minute of arc of latitude along a meridian.

That definition is what makes it useful: a degree of latitude is 60 nautical miles, so distance can be read straight off a chart's latitude scale.

Answer: C

A solar eclipse occurs when the moon comes between the sun and the earth, casting its shadow on the earth's surface.

This can happen only at new moon. When the earth comes between the sun and the moon, the moon passes into the earth's shadow and there is a lunar eclipse instead.

Answer: A

Lichens are the best indicators of air pollution, particularly sulphur dioxide.

They take their minerals directly from the air and rain, having no roots and no protective cuticle, so pollutants accumulate in them. Sensitive species disappear from city centres, and the pattern of what survives maps the pollution.

Answer: C

The decibel measures the loudness or intensity of sound.

It is logarithmic: 10 dB is a tenfold increase in intensity, so the scale can cover the enormous range the ear handles. Frequency, which determines pitch, is measured in hertz instead - cycles per second.