Science & Technology Mixed Quiz: Set 29

The correct answer is B, El Salvador. The Central American country passed a Bitcoin Law in June 2021 and became, in September 2021, the first state anywhere to give bitcoin the status of legal tender alongside the United States dollar, which it already used as its currency. The step drew wide comment because it made a privately created token acceptable in payment of debts in a sovereign country, and international financial institutions warned about the risk to stability. Option A is wrong because Venezuela issued a state-backed token called the petro but never made bitcoin legal tender. Option C is wrong because Nigeria launched a central bank digital currency, the eNaira, which is the opposite approach, a sovereign digital currency rather than a private token. Option D is wrong because Switzerland, although friendly to the industry, treats these tokens as assets and not as legal tender.

The correct answer is B, 2019. NewSpace India Limited was incorporated in 2019 as a public sector undertaking under the Department of Space, with its registered office at Bengaluru. It runs demand-driven missions, owns and operates satellites, has launch vehicles built by Indian industry and transfers ISRO's technology to private firms. Option A is wrong because 1992 is the year Antrix Corporation, the older commercial arm of the department, was set up; a question often pairs the two years to see whether a candidate can tell the two companies apart. Option C is wrong because 2020 is the year the space sector reforms were announced and IN-SPACe was created. Option D is wrong because 2023 is the year the Indian Space Policy was approved, which defined the roles of ISRO, NSIL and IN-SPACe.

The correct answer is C, 35,786 km. Only at this height does a satellite in a circular equatorial orbit take exactly one sidereal day to complete a revolution, which is the condition for appearing stationary above one point on the Earth. The figure is commonly rounded to about 36,000 kilometres, and both forms are accepted in answers.

Option A, 3,578 km, is the same digits with a misplaced decimal and is included to catch hasty reading. Option B, 20,200 km, is the altitude of the Global Positioning System satellites, which lie in medium Earth orbit and have a period of about twelve hours, not one day. Option D is far too high and is closer to the scale used for Lagrange point missions; India's Aditya-L1, for instance, sits about 1.5 million kilometres away at the Sun-Earth point L1. Remember the trio: low Earth orbit up to 2,000 km, medium Earth orbit beyond that, and geostationary at 35,786 km.

The correct answer is B, SHA-256. Bitcoin uses the SHA-256 hash function, part of the Secure Hash Algorithm family, which turns an input of any length into a fixed output of two hundred and fifty-six bits. The function is one-way, so the input cannot be derived from the output, and it is collision resistant, so two different inputs practically never give the same hash; mining consists of searching for a nonce that makes the block hash fall below a target value. Option A is wrong because MD5 is an older and now broken hash function, no longer considered secure. Option C is wrong because AES is a symmetric encryption cipher, not a hash function, and encryption is reversible with the key while a hash is not. Option D is wrong because RSA is a public key encryption and signature algorithm; bitcoin signs transactions with elliptic curve cryptography, not RSA.

The correct answer is C, Dakshin Gangotri. It was built during the Indian expedition of 1983 to 1984 in Queen Maud Land and was India's first permanent base on the continent. Because it stood on a floating ice shelf, the movement of the ice and the steady accumulation of snow buried it, and it was given up as a working station in 1990, after which it has served only as a supply base and transit camp.

Option A, Maitri, is the second station, commissioned in 1989, and is the answer most candidates give because it is the station they have heard of. Option B, Bharati, is the third station, commissioned in 2012. Option D, Himadri, is not in Antarctica at all; it is India's Arctic station in Svalbard, Norway, and it is placed here precisely to catch the confusion between the two poles. The order to remember is Dakshin Gangotri, then Maitri, then Bharati.

The correct answer is C, 916. Fineness is the carat value divided by 24 and multiplied by one thousand, so 22 divided by 24 gives 0.916 and the article is marked 22K916, meaning 91.6 per cent gold. This is the usual grade for Indian jewellery because pure gold is too soft to hold a setting. Option A is wrong because 750 is the mark for 18 carat gold, which is 75 per cent gold. Option B is wrong because 833 corresponds to 20 carat gold, at 83.3 per cent. Option D is wrong because 999 is the mark for 24 carat, that is pure gold, which is sold as coins and bars rather than jewellery. Learn the ladder 999, 958, 916, 833, 750 and 585 against 24, 23, 22, 20, 18 and 14 carat, because papers ask it in either direction.

The correct answer is C, 2023. The Indian Space Policy was approved in 2023 and set out in writing the division of work that the reforms of 2020 had begun: private companies, called non-government entities, may carry out the whole range of space activities; ISRO is to concentrate on research and advanced missions; NSIL is to act commercially in the demand-driven mode; and IN-SPACe is to be the single window for authorisation. Option A is wrong because 2019 is the year NSIL was incorporated. Option B is wrong because 2020 is the year the reforms were announced and IN-SPACe was created, before any policy document existed. Option D is wrong because 2024 is the year of the foreign direct investment amendment for the space sector, a separate decision taken by the Union Cabinet.

The correct answer is A, Kavalur in Tamil Nadu. In 1977 astronomers watched Uranus pass in front of a distant star from the observatory in the Javadi hills, and the dips in the star's light before and after the planet itself crossed showed that rings surround Uranus. The site later received the 2.34 metre telescope named after Vainu Bappu, who founded the observatory, and it belongs to the Indian Institute of Astrophysics. B is a solar observatory and could not have made such an observation. C was developed as an observing site only in the closing years of the twentieth century, two decades after the event. D hosts optical telescopes but had no part in this particular discovery. The method used, watching a star dim as a body passes in front of it, is called occultation.

The correct answer is C, Both 1 and 2. LiFi (Light Fidelity) sends data wirelessly by switching LED light on and off far too fast for the eye to notice, and it can be many times faster than WiFi.

The idea was popularised by Professor Harald Haas of the University of Edinburgh in 2011. A LiFi bulb flickers at very high frequency, and a photodetector reads these changes as binary data. Because visible light has a far wider spectrum than the radio waves used by WiFi, laboratory tests have reached speeds many times higher than WiFi. Light cannot pass through walls, which limits range but makes the signal harder to intercept and free of radio interference, useful in hospitals and aircraft.

A is wrong because statement 2 is also correct.

B is wrong because statement 1, the use of light, is the very basis of LiFi.

D is wrong because both statements describe LiFi correctly.

Exam tip: WiFi uses radio waves; LiFi uses visible light from LEDs and cannot pass through walls.

The correct answer is C, computer numerical control milling. Milling on a computer-controlled machine is a subtractive process: a rotating cutter removes material from a solid block until the shape remains, so no layers are added. Option A is wrong because fused deposition modelling is an additive process in which a heated nozzle extrudes a thermoplastic filament layer by layer. Option B is wrong because selective laser sintering is additive too, fusing grains of polymer powder together with a laser where the object is to be solid. Option D is wrong because stereolithography, the oldest of the three, is additive: a laser cures liquid resin point by point. Slipping a machining process in among printing processes is the standard way this question is set. It is worth noting that additive and subtractive methods are often combined in practice, a printed part being finished on a milling machine to get an accurate surface.

The correct answer is B. A fifty-one per cent attack is one in which a single party commands a majority of the resource that decides consensus, which is the mining power in a proof of work chain and the staked coins in a proof of stake chain. With that majority the attacker can build the longest chain, so it can exclude or reorder transactions and reverse its own recent payments to spend the same coins twice. It cannot forge coins out of nothing or move coins from other people's addresses, because those still require the owner's private key. Option A is wrong because guessing private keys is a cryptographic attack on individual users, not a consensus attack. Option C is wrong because merely holding coins gives no power over block production in a proof of work chain. Option D is wrong because shutting down nodes is a denial of service attack and does not let the attacker rewrite the ledger.

The correct answer is B, the Andaman and Nicobar Command, Port Blair. It is the only command in which units of the Army, the Navy and the Air Force work under a single commander-in-chief, an arrangement adopted because the islands lie far from the mainland and guard the approaches to the Malacca Strait. Option A, the Western Naval Command at Mumbai, is a naval command and the home of the carrier fleet on the west coast. Option C, the Eastern Naval Command at Visakhapatnam, is the Navy's command on the east coast. Option D, the Southern Naval Command at Kochi, is the Navy's training command. All three of the latter are naval commands alone, which is the distinction the question tests, and the Strategic Forces Command, which handles nuclear weapons, is a separate tri-service body rather than a geographical command.

The correct answer is B, one sidereal day, 23 hours 56 minutes 4 seconds. A geostationary satellite must match the rotation of the Earth with respect to the distant stars, and that rotation takes one sidereal day. Matching the solar day of twenty-four hours would leave the satellite drifting slowly, because the solar day includes the extra turn needed to face the Sun again as the Earth moves along its orbit.

Option A, exactly 24 hours, is the answer most candidates give and is accepted loosely in general conversation, but in a careful question the sidereal figure is the right one. Option C, 12 hours, is roughly the period of a navigation satellite in medium Earth orbit and of a Molniya orbit. Option D, about 90 minutes, is the period of a satellite in low Earth orbit, such as a space station at around 400 kilometres. The rule behind all of this is that orbital period increases with orbital height.

The correct answer is C, a distributed denial of service attack. A denial of service attack exhausts a server's capacity with a flood of requests, and when the flood is generated from many machines at once, often a botnet of infected computers, it is called distributed. The goal attacked here is availability, the third limb of the CIA triad. Option A is wrong; phishing is a fraudulent message imitating a trusted institution in order to obtain a password or card number. Option B is wrong because SQL injection inserts malicious database commands through an input field to read or alter stored data, which attacks confidentiality and integrity. Option D is wrong since a man-in-the-middle attack intercepts traffic between two parties without either of them knowing. The Cyber Swachhta Kendra exists to clean the botnets used in such attacks.

The correct answer is B, Schirmacher Oasis in Queen Maud Land. Maitri was commissioned in 1989 on the rocky Schirmacher Oasis, a narrow ice-free strip, next to the freshwater lake named Priyadarshini. Standing on rock rather than on ice is precisely why Maitri has survived while the earlier station on the ice shelf did not.

Option A, Larsemann Hills, is the site of Bharati, India's third station, commissioned in 2012 on the east Antarctic coast, and swapping the two sites is the commonest error here. Option C, Ny-Alesund in Svalbard, is in the Arctic and is the site of Himadri, not of any Antarctic station. Option D, the Ross Ice Shelf, is a well known Antarctic feature on the other side of the continent where several other countries have bases, but India has never built there. Fix the pair: Maitri at Schirmacher, Bharati at Larsemann.

The correct answer is A, Jagadish Chandra Bose. He designed the crescograph, which magnifies the growth of a plant many thousand times so that it can be recorded, and used it and related instruments to argue that plants respond to light, heat, touch and other stimuli much as animals do. He also did pioneering work on very short radio waves before Marconi transatlantic experiments, and he founded the Bose Institute at Kolkata in 1917. Option B is wrong; Prafulla Chandra Ray, the father of Indian chemistry, discovered mercurous nitrite in 1896 and founded Bengal Chemical and Pharmaceutical Works. Option C is wrong; Birbal Sahni was a palaeobotanist who studied the fossil plants of India, and the institute at Lucknow carries his name. Option D is wrong; Salim Ali, the birdman of India, conducted the systematic bird surveys of the subcontinent and wrote The Book of Indian Birds.

The correct answer is C, Tamil Nadu. Kulasekarapattinam lies in the Thoothukudi district of Tamil Nadu, on the southern coast, and is being developed as a spaceport for small satellite launch vehicles. Its advantage is geographical: a rocket launched southward from there flies straight out over the sea, while one launched from Sriharikota has to turn to avoid passing over Sri Lanka, and avoiding that turn saves fuel and allows a heavier payload. Option A is wrong because Andhra Pradesh is where the existing spaceport, the Satish Dhawan Space Centre at Sriharikota, stands. Option B is wrong because Kerala hosts the Vikram Sarabhai Space Centre and the Thumba Equatorial Rocket Launching Station, used for sounding rockets, not orbital launches. Option D is wrong because Odisha has the Chandipur integrated test range, which is a missile testing range of the defence establishment.

The correct answer is B, sun-synchronous polar orbit. Such an orbit is near-polar, typically 600 to 900 kilometres high with an inclination of about 98 degrees, which makes it retrograde. Its plane precesses at the same rate at which the Earth revolves round the Sun, so the satellite crosses a given latitude at the same local solar time on every pass. Shadows and illumination are therefore comparable, which is what makes change detection possible. India's Cartosat, Resourcesat and Oceansat satellites use it.

Option A, geostationary orbit, gives a constant view of one hemisphere and suits communication and weather satellites such as INSAT, but it is far too high for detailed mapping. Option C, Molniya orbit, is a highly elliptical orbit inclined at about 63.4 degrees used to give long dwell time over high latitudes. Option D, graveyard orbit, is not a working orbit at all; it is a disposal orbit above the geostationary belt where retired satellites are parked.

The correct answer is C, 2012. Bharati was commissioned in 2012 at the Larsemann Hills on the coast of east Antarctica, roughly three thousand kilometres from Maitri. Having two stations so far apart lets Indian scientists study two very different sectors of the continent in the same summer season, which was the main reason for building it.

Option A, 1989, is the year Maitri was commissioned. Option B, 2008, is the year Himadri, India's Arctic station in Svalbard, was opened, so it belongs to the other pole. Option D, 2016, is the year the Himansh high-altitude glaciology station was set up in the Spiti area of Himachal Pradesh. All four years belong to this topic, which is why the question works; the chain to memorise is 1983-84 Dakshin Gangotri, 1989 Maitri, 2008 Himadri, 2012 Bharati, 2014 IndARC and 2016 Himansh.

The correct answer is B, Arthur C. Clarke. The British science fiction writer and engineer set out in 1945 how three satellites placed in a circular equatorial orbit at about 36,000 kilometres could relay radio signals to almost the whole inhabited world. The geostationary orbit is therefore also called the Clarke Orbit, and the ring of satellites in it is sometimes called the Clarke Belt.

Option A, Isaac Asimov, was a famous science fiction writer but is not connected with this proposal. Option C, Konstantin Tsiolkovsky, was the Russian pioneer who worked out the rocket equation and the theory of spaceflight decades earlier, but not the geostationary relay idea. Option D, Jules Verne, imagined a journey to the Moon in the nineteenth century, long before orbital mechanics of this kind were applied. Clarke is the name to remember with 1945 and 35,786 kilometres.