UPSC CAPF 2018 Previous Year GK Questions with Answers

The correct answer is A, 2 and 1. For a 4d orbital, n = 4 and l = 2, which gives l = 2 angular nodes and n − l − 1 = 1 radial node.

A node is a region where the probability of finding the electron is zero. Angular nodes are planes or cones through the nucleus, and their number equals the azimuthal quantum number l. Radial nodes are spherical shells, and their number is n − l − 1. The total number of nodes is always n − 1. For 4d: l = 2 for any d orbital, so 2 angular nodes; radial nodes = 4 − 2 − 1 = 1; total = 3, which equals n − 1. In the same way 3d has 2 angular and 0 radial nodes, and 2s has 0 angular and 1 radial node.

B is wrong: it reverses the two values.

C is wrong: 3 angular nodes belong to an f orbital (l = 3), not a d orbital.

D is wrong: 4 angular nodes would need l = 4, a g orbital, and the total of 4 exceeds n − 1 = 3.

Exam tip: angular nodes = l, radial nodes = n − l − 1, total nodes = n − 1.

The correct answer is B, lowers the boiling point of the liquid. A liquid boils when its vapour pressure equals the pressure above it, so less outside pressure means boiling starts at a lower temperature.

As a liquid is heated, its vapour pressure rises. Boiling begins at the temperature where this vapour pressure matches the external pressure. At sea level, with about 101.3 kPa of pressure, water boils at 100 °C. High in the mountains the air pressure is lower, so water boils at around 70 to 90 °C, which is too cool to cook rice or pulses quickly. A pressure cooker does the opposite: it raises the pressure to about twice the normal value, so water boils near 120 °C and food cooks faster.

A is wrong: raising the pressure, not lowering it, raises the boiling point.

C is wrong: boiling point depends directly on the outside pressure.

D is wrong: with a lower boiling point the liquid reaches boiling sooner, not later.

Exam tip: low pressure, low boiling point (hills); high pressure, high boiling point (pressure cooker).

The correct answer is A, 1 and 3. A compound microscope uses two convex lenses, and its magnification depends on the tube length.

The objective is a convex lens of very short focal length that forms a real, enlarged image of the specimen. The eyepiece is also a convex lens and works like a magnifying glass on that image. The total magnification is roughly (L/fo) × (D/fe), where L is the tube length, D is 25 cm, the least distance of distinct vision, and fo and fe are the focal lengths of the objective and eyepiece. So a longer tube gives more magnification, while a longer focal length gives less.

B is wrong: statement 3 is true, but statement 1 is also true, so 3 alone is incomplete.

C is wrong: statement 4 is false, because the eyepiece is convex, not concave.

D is wrong: statement 2 is false, since magnification falls as the objective's focal length rises, and statement 4 is false as well.

Exam tip: microscope = two convex lenses, objective of short focal length; telescope objective has a long focal length.

The correct answer is C, total internal reflection. Light inside the fibre strikes the boundary at more than the critical angle, so it is reflected back again and again instead of escaping.

An optical fibre has a glass core surrounded by cladding of slightly lower refractive index. Total internal reflection happens when light travels from a denser to a rarer medium and the angle of incidence is greater than the critical angle. Each time the signal meets the core-cladding boundary it is fully reflected, so it zigzags along the fibre with very little loss, even around gentle bends. This is why fibres carry internet and telephone data over long distances and are used in endoscopes.

A is wrong: interference is the overlapping of waves to form bright and dark bands.

B is wrong: scattering spreads light out, as in the blue sky, and is a source of loss in a fibre.

D is wrong: refraction lets light pass out of the core; the fibre works because light does not refract out.

Exam tip: two conditions for total internal reflection are denser to rarer medium and angle above the critical angle; examples are optical fibre, sparkling diamond and mirage.

The correct answer is A, the Arabian Sea exhibits a high rate of evaporation and a low influx of fresh water. Salinity rises where water leaves as vapour and falls where fresh water is added. The air over the Arabian Sea is dry and hot, evaporation is heavy, rainfall is modest and the only large river reaching it is the Indus, so the salt that stays behind keeps surface salinity around 36 parts per thousand. The Bay of Bengal gets the Ganga, Brahmaputra, Mahanadi, Godavari and Krishna along with very heavy monsoon rain, and all that fresh water dilutes it to about 33 parts per thousand. Option B is wrong because the Arabian Sea is in fact the deeper of the two basins, and depth by itself does not decide salinity. Option C is wrong because the Bay of Bengal is the more enclosed of the two, yet it is the less saline. Option D is wrong because the Arabian Sea receives less rainfall, and rain lowers salinity instead of raising it. Exam tip: evaporation raises salinity; river water and rainfall lower it.

The correct answer is B, Emerald. Emerald is the deep green variety of the mineral beryl, a beryllium aluminium silicate, so beryllium is part of its very formula. Traces of chromium, and sometimes vanadium, give the stone its green colour. Beryl is the chief ore of beryllium, a light, stiff metal used in X-ray windows, aerospace alloys and nuclear reactors; aquamarine is the pale blue variety of the same mineral. Option A is wrong because topaz is an aluminium silicate carrying fluorine and hydroxyl groups, with no beryllium in it. Option C is wrong because ruby is corundum, that is aluminium oxide, which turns red because of chromium impurity. Option D is wrong because blue sapphire is the same corundum, coloured blue by traces of iron and titanium. So ruby and sapphire are two colours of one mineral, while emerald belongs to a different family altogether. Exam tip: emerald = beryl (beryllium); ruby and sapphire = corundum (aluminium oxide).

The correct answer is D, Dual Government. A dual government, one at the centre and one in the units, is the common feature of every federation, so India and the USA do not differ on this point. Both countries divide powers between a national government and state governments through a written constitution, and both let courts settle disputes about that division. The other three features are exactly where the two systems part company, because India has a federation with a strong unitary bias. Option A is wrong because every American state sends two members to the Senate regardless of size, while seats in the Rajya Sabha are allotted according to a state’s population, so representation is unequal. Option B is wrong because an American citizen is a citizen of both the Union and a state, while India gives only single citizenship. Option C is wrong because the USA has separate federal and state courts, while India has one integrated judiciary headed by the Supreme Court. Exam tip: India — single citizenship, integrated judiciary, unequal Rajya Sabha seats.