UPSC CAPF 2020 Previous Year GK Questions with Answers

The correct answer is D, Annelida. Annelids such as the earthworm, leech and Nereis are the first coelomates in the usual sequence: their body cavity is lined on all sides by mesoderm.

Zoologists group animals by their body cavity. Acoelomates have no cavity at all; pseudocoelomates, such as roundworms (Aschelminthes), have a cavity only partly lined by mesoderm; true coelomates have a cavity fully lined by mesoderm, which gives room for organs to grow and move. Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata and Chordata are all coelomates. In the earthworm, the fluid in this coelom also acts as a hydrostatic skeleton for burrowing.

A is wrong: Porifera, the sponges, are at the cellular level of organisation and have no true tissues or coelom.

B is wrong: Platyhelminthes, the flatworms such as tapeworm and liver fluke, are acoelomate.

C is wrong: Cnidaria such as Hydra and jellyfish are diploblastic, with only a gut cavity and no coelom.

Exam tip: acoelomate = flatworms; pseudocoelomate = roundworms; coelomate starts with Annelida.

The correct answer is C, Polyaromatic hydrocarbons. Polyaromatic hydrocarbons are soot-related pollutants from incomplete burning; they are not among the gases that make up photochemical smog.

Photochemical smog forms on warm, sunny days in cities with heavy traffic. Vehicle exhaust releases nitric oxide and unburnt hydrocarbons; nitric oxide turns into nitrogen dioxide, which sunlight splits to free oxygen atoms that make ozone. Ozone and nitrogen oxides then react with hydrocarbons to form peroxyacetyl nitrate (PAN), formaldehyde and acrolein. The mix irritates the eyes and lungs and damages plants. It is oxidising, unlike the reducing classical smog of smoke and sulphur dioxide seen in London.

A is wrong: ozone is the main oxidant in photochemical smog.

B is wrong: PAN is a typical secondary pollutant of photochemical smog and a strong eye irritant.

D is wrong: nitric oxide from vehicle engines is the starting point of the smog reactions.

Exam tip: photochemical smog = NO, NO2, O3, PAN, aldehydes (oxidising, Los Angeles type); classical smog = smoke + SO2 (reducing, London type).

The correct answer is B, Ion-exchange. An ion-exchange resin or zeolite swaps the calcium and magnesium ions that cause permanent hardness for sodium or hydrogen ions.

Permanent hardness comes from the chlorides and sulphates of calcium and magnesium, which do not break down on heating. In the zeolite (permutit) process, sodium aluminium silicate takes up Ca2+ and Mg2+ and gives out Na+, which does not harden water; the exhausted zeolite is renewed by washing it with brine. Synthetic resins work the same way. Washing soda and Calgon also remove permanent hardness.

A is wrong: boiling removes only temporary hardness, by turning soluble bicarbonates into insoluble carbonates.

C is wrong: lime treatment, Clark's method, also removes only temporary (bicarbonate) hardness.

D is wrong: bubbling sulphur dioxide only makes the water acidic; it does not take out calcium or magnesium.

Exam tip: temporary hardness = bicarbonates, removed by boiling or Clark's lime; permanent = chlorides and sulphates, removed by washing soda, Calgon or ion exchange.

The correct answer is C, Thiourea (accelerator). Accelerators speed up the vulcanisation of rubber; they are not a part of paint.

An oil paint is made of a pigment that gives colour and covering power, a vehicle or drying oil such as linseed oil that binds the film, a thinner that makes it easy to spread, a drier that speeds up hardening, fillers or extenders that add body, and an anti-skinning agent that stops a skin forming in the tin. Titanium dioxide is the most widely used white pigment, turpentine is the classic thinner, and polyhydroxy phenols are used as anti-skinning agents. Thiourea and similar compounds belong to rubber technology, where accelerators shorten the time sulphur takes to cross-link rubber.

A is wrong: turpentine oil is a standard thinner in paint.

B is wrong: polyhydroxy phenols are used in paint as anti-skinning agents.

D is wrong: titanium dioxide is the main white pigment in paints.

Exam tip: paint = pigment + vehicle (linseed oil) + thinner (turpentine) + drier + filler + anti-skinning agent.

The correct answer is A, fireworks to make a bright white light. Magnesium burns in air with a dazzling white flame, which is why it goes into fireworks, sparklers and flares.

When magnesium ribbon is heated it reacts with oxygen to form white magnesium oxide (2Mg + O2 → 2MgO), giving out intense heat and brilliant white light, including ultraviolet. Pyrotechnic makers add magnesium or magnesium-aluminium alloy powder to brighten colours and produce white sparks; the same property was used in early photographic flash powder. Magnesium is also the central atom of chlorophyll and a light metal used in alloys for aircraft and car parts.

B is wrong: gemstones are minerals such as corundum, beryl or diamond, not magnesium metal.

C is wrong: the alimentary canal is examined with a barium meal, using barium sulphate, which shows up in X-rays.

D is wrong: water is purified with chlorine, bleaching powder, alum or ozone, not magnesium.

Exam tip: magnesium = white flame and the centre of chlorophyll; barium = green flame and the barium meal; strontium = red flame.

The correct answer is C. The third law does not make one force the cause and the other the effect; action and reaction arise together, at the same instant.

Newton's third law says that to every action there is an equal and opposite reaction. The two forces act on two different bodies, are equal in size, opposite in direction and simultaneous. Because neither comes first, the words action and reaction are only labels; either force can be called the action. This is also why forces always come in pairs in nature.

A is correct and so not the answer: a force is always an interaction between two bodies, so it never occurs alone.

B is correct and so not the answer: the stone pulls the Earth upwards with the same force; the Earth barely moves because its mass is enormous.

D is correct and so not the answer: it is the accurate reading of the law, that action and reaction are simultaneous, with no cause and effect between them.

Exam tip: action and reaction are equal, opposite, simultaneous and act on different bodies, so they never cancel each other.

The correct answer is C, Doppler effect. A speed radar measures how much the frequency of its reflected wave changes, and that change depends on the speed of the vehicle.

The Doppler effect, described by Christian Doppler in 1842, is the apparent change in the frequency of a wave when the source and the observer move relative to each other. The police gun sends out radio waves of a fixed frequency; a car coming towards it reflects them at a higher frequency, a car moving away at a lower one. The device converts this frequency shift into the speed of the vehicle. The same idea explains the falling pitch of a passing train's horn and the red shift of distant galaxies.

A is wrong: the Raman effect is the scattering of light by molecules with a change of wavelength, found by C. V. Raman in 1928.

B is wrong: induction is about producing current by a changing magnetic field.

D is wrong: Coulomb's law gives the force between electric charges.

Exam tip: speed gun, passing horn and red shift of galaxies all use the Doppler effect.

The correct answer is B, inter cropping. In intercropping two or more crops are grown together on the same field at the same time, but sown in a definite pattern of rows, such as a few rows of soyabean between rows of maize, or bajra with lobia. The crops chosen have different nutrient needs and different rooting depths, so they use the soil, sunlight and water better, pests spread more slowly, and if one crop fails the farmer still has the other. It differs from mixed cropping, where the seeds of two crops are simply mixed and broadcast with no row pattern. Option A is wrong because crop rotation means growing different crops one after another on the same field in successive seasons, to restore fertility. Option C is wrong because alternate cropping is not the name for sowing two crops side by side in the same season. Option D is wrong because kharif names a season, the monsoon crop sown in June and July, not a method of cropping. Exam tip: mixed cropping has no rows, intercropping has definite rows, rotation is one crop after another.

The correct answer is D, Neon. When electricity is passed through a sealed tube holding neon at low pressure, the gas atoms are excited and give out a bright orange-red glow, which is why advertising signs are still called neon signs. Neon is a noble gas discovered in 1898 by Ramsay and Travers; it is chemically inert, forms no ordinary compounds, and is also used in voltage testers, high-voltage indicators and lightning arresters. Every gas glows in its own colour in a discharge tube, and that colour is the fingerprint of its atomic energy levels. Option A is wrong because helium gives a pale pinkish-white glow and is better known for filling balloons and airships. Option B is wrong because argon glows a pale violet-blue and is used to fill electric bulbs and to shield welding. Option C is wrong because nitrogen glows bluish, and its common uses are as an inert packing gas and as a liquid coolant. Exam tip: neon gives red light in a discharge tube, while argon is the gas that fills ordinary electric bulbs.

The correct answer is D, Micro, Small and Medium Enterprises. The expression comes from the Micro, Small and Medium Enterprises Development Act, which came into force on 2 October 2006 and gave the sector its first statutory definition, replacing the older language of small scale and ancillary industrial undertakings.

Option A is wrong because the first category is micro, not medium; the three categories in ascending order are micro, small and medium. Option B is wrong for the same reason in reverse: the third word is medium and not marginalized, and no Indian law uses the term marginalized enterprise. Option C is wrong because strategic is not a category of enterprise in the Act at all. Since this is the easiest question the sector can yield, read the options to the end: all four begin with words that look plausible, and only one gives the three categories in the correct order.

The correct answer is They may not be used for determining constitutionality of laws, because this statement is false. The Supreme Court has held that when a court tests whether a law is constitutional, and finds that the law gives effect to a Fundamental Duty, it may treat the law as "reasonable" under Article 14 or Article 19 and uphold it. So the duties can indeed help determine the constitutionality of laws, even though they cannot themselves be enforced.

The other three statements are correct, which is what makes the question hard. The Fundamental Duties were not part of the original Constitution of 1950; they were added by the 42nd Amendment in 1976. Safeguarding public property and abjuring violence is a Fundamental Duty, clause (i) of Article 51A. And the duties are not enforceable through writs, because they are non-justiciable: no court can order a citizen to perform them, though Parliament can enforce them through ordinary laws. In a "NOT correct" question, test each statement separately before choosing.