General Science Mixed Quiz: Set 5

The correct answer is B, distance. A light year is the distance that light, moving at about three lakh kilometres per second, covers in one year, which works out to roughly 9.46 trillion kilometres. It is used for the enormous distances between stars, where kilometres would run to unmanageable numbers.

Option A is the trap built into the name; the word year refers to the time taken by the light, not to the quantity measured. Option C, speed, has its own units such as metres per second. Option D, brightness, is measured by other quantities altogether, such as magnitude in astronomy. Two more distance units belong with this one: the astronomical unit, the mean distance between the Earth and the Sun, and the parsec, which equals about 3.26 light years.

The correct answer is D, Four. In diamond every carbon atom is joined to four other carbon atoms by strong covalent bonds. These bonds point towards the corners of a tetrahedron and build a rigid three-dimensional network that runs through the whole crystal. That network makes diamond the hardest natural substance, which is why it is used in cutting and drilling tools. Since all four valence electrons are used in bonding, no free electrons are left, so diamond does not conduct electricity. In graphite, the other common form of carbon, each atom bonds to only three others in flat hexagonal layers, and the spare electron lets graphite conduct. A is wrong because two bonds per carbon cannot build a solid network. B is wrong because carbon has a valency of four and cannot form five bonds. C is wrong because three bonds per atom describes graphite, not diamond. Exam tip: diamond = 4 bonds, hard, insulator; graphite = 3 bonds, soft, conductor.

The correct answer is A, Total internal reflection. When light travels from a denser medium to a rarer one and strikes the boundary at an angle greater than the critical angle, it does not pass out at all but is reflected completely back. An optical fibre uses exactly this. It has a thin glass or plastic core of higher refractive index, covered by a cladding of lower refractive index, so light entering one end keeps bouncing off the walls and travels long distances, even around bends, with very little loss. That is why fibres carry internet and telephone signals and are used in endoscopes to see inside the body. The Indian-born physicist Narinder Singh Kapany is called the father of fibre optics. Option B is wrong because diffraction is the bending of light around small obstacles or through narrow slits. Option C is wrong because scattering spreads light in many directions, which makes the sky look blue. Option D is wrong because refraction is only the bending of light as it enters a new medium, while a fibre works by stopping light from escaping. Exam tip: optical fibre, mirage and a sparkling diamond all work by total internal reflection.

The correct answer is C, more than the atmospheric pressure. Air always moves from a region of higher pressure to one of lower pressure, so it flows out of the lungs only when the pressure inside them rises above that of the outside air. During expiration the diaphragm relaxes and moves up into its dome shape, and the intercostal muscles between the ribs relax, so the ribs move down and inward. This reduces the volume of the chest cavity, which raises the pressure in the lungs and pushes the air out. Inspiration is the reverse: the diaphragm contracts and flattens, the chest cavity grows, lung pressure falls below atmospheric pressure and air rushes in. Option A is wrong because when the pressures are equal no air moves; this happens for a moment between breaths. Option B is wrong because lower pressure inside the lungs draws air in, which is inspiration. Option D is wrong because contraction of the diaphragm enlarges the chest and causes inspiration, not expiration. Exam tip: inspiration means the diaphragm contracts and lung pressure falls; expiration means it relaxes and lung pressure rises.

The correct answer is A, one coulomb per second. Electric current is the rate of flow of electric charge, written as I = Q/t, so one ampere flows when one coulomb of charge passes through a cross-section of a conductor in one second. One coulomb is the charge carried by about 6.25 × 10^18 electrons, so even a small current means a huge number of moving electrons. The ampere is one of the seven SI base units, and it is named after the French scientist André-Marie Ampère. Current is measured with an ammeter, which is always connected in series in a circuit, and small currents are expressed in milliamperes or microamperes. Option B is wrong because volt per second is not a unit of current; the volt measures potential difference. Option C is wrong because one joule per coulomb is the definition of one volt, the unit of potential difference. Option D is wrong because second per coulomb is the reverse of current and is not used as a unit at all. Exam tip: ampere = coulomb per second, volt = joule per coulomb, ohm = volt per ampere.

The correct answer is C, Only (b). Of the three, only citrus canker is caused by bacteria; rust of wheat is caused by a fungus and yellow vein mosaic of bhindi by a virus. Citrus canker produces raised, corky brown spots on the leaves, twigs and fruits of lemon, orange and other citrus plants, and it spreads through the air. Rust of wheat forms reddish-brown powdery patches on the leaves and stems, which is how it got its name. Yellow vein mosaic turns the veins of bhindi, or okra, leaves yellow, and insects carry the virus from plant to plant. NCERT's Class 8 science book gives exactly these three as its examples of bacterial, fungal and viral diseases of plants. A is wrong because yellow vein mosaic is a viral disease, not a bacterial one. B is wrong because it adds rust of wheat, which is a fungal disease. D is wrong because it adds the viral yellow vein mosaic. Exam tip: citrus canker, bacteria; rust of wheat, fungus; yellow vein mosaic of bhindi, virus.

The correct answer is D, Hg. Mercury (Hg) belongs to group 12, not group 11. Group 11 of the modern periodic table holds copper (Cu, atomic number 29), silver (Ag, 47) and gold (Au, 79). These three are called the coinage metals because coins were made from them; each has one electron in its outermost s orbital, which makes them soft and shiny, and silver and copper are the best conductors of electricity of all metals. Mercury sits right next to gold in period 6 but in group 12, together with zinc and cadmium, and it is the only metal that is liquid at room temperature. A is wrong because silver is a group 11 metal. B is wrong because gold is also in group 11. C is wrong because copper heads group 11. Exam tip: Group 11 = Cu, Ag, Au (coinage metals); Group 12 = Zn, Cd, Hg; the liquid metal mercury is never a coinage metal.

The correct answer is C, Abscisic acid. It is the main growth inhibitor among plant hormones and works against the growth promoters. Abscisic acid, or ABA, is called the stress hormone because it helps plants survive drought, cold and salt: it makes the stomata close to save water, keeps seeds and buds dormant so they do not sprout in bad weather, and helps leaves and fruits to age and fall. So when a question asks which hormone slows or stops growth, ABA is the answer; ethylene is the other hormone linked with ageing and ripening. A is wrong, because auxins promote growth by making cells elongate, and they make shoots bend towards light. B is wrong, because cytokinins promote cell division and delay the ageing of leaves. D is wrong, because gibberellins promote stem elongation, break seed dormancy and are sprayed on grapes to increase their size. Exam tip: the growth promoters are auxin, gibberellin and cytokinin; the inhibitor is abscisic acid, the stress hormone.

The correct answer is A, CH₄ + 2O₂ → CO₂ + 2H₂O. Combustion means burning in oxygen, and complete burning of methane gives carbon dioxide, water, heat and light. The equation is balanced: one carbon, four hydrogen and four oxygen atoms on each side. Methane is the simplest hydrocarbon and the main gas in natural gas, CNG and biogas, which is why it burns with a clean blue flame in stoves and vehicles. When oxygen is short, burning is incomplete and poisonous carbon monoxide forms instead of carbon dioxide. B is wrong because it is a substitution reaction: in sunlight chlorine replaces a hydrogen atom of methane, and nothing burns. C is wrong because it is not balanced and shows carbon monoxide, the product of incomplete burning. D is wrong because methane reacting with steam, not oxygen, to give carbon monoxide and hydrogen is steam reforming, an industrial way to make hydrogen. Exam tip: complete combustion of any hydrocarbon gives CO₂ + H₂O + energy.

The correct answer is D, Sickle cell anaemia, Haemophilia, Down syndrome. All three are genetic disorders, caused by changes in genes or chromosomes and passed on through birth, not by germs. Sickle cell anaemia is an autosomal recessive disease in which a single change in the haemoglobin gene makes red blood cells sickle-shaped. Haemophilia is a sex-linked recessive disorder carried on the X chromosome, in which blood does not clot properly; it mostly affects males, and it is called the royal disease because it spread among Queen Victoria's descendants. Down syndrome is a chromosomal disorder caused by an extra copy of chromosome 21, also called trisomy 21. Option A is wrong because AIDS is caused by the HIV virus and is not inherited through genes. Option B is wrong because AIDS and Hepatitis B are viral infections, and most cancers come from mutations acquired during life. Option C is wrong because Hepatitis B is a viral infection, even though haemophilia and colour blindness are genetic. Exam tip: genetic disorders include sickle cell anaemia, haemophilia, colour blindness, thalassaemia and Down syndrome.

The correct answer is B, H3O+. A hydrogen ion (H+) is just a bare proton, so it cannot stay alone in water. It at once attaches itself to a water molecule and forms the hydronium ion, H3O+. So when an acid such as hydrochloric acid dissolves in water, it really produces H3O+ ions, and these give the solution its acidic nature. Without water, acids do not show acidic behaviour, which is why dry HCl gas does not change the colour of dry blue litmus paper. Option A is wrong because HO- (OH-) is the hydroxide ion, which bases give in water. Option C is wrong because H2 is hydrogen gas, a neutral molecule, not an ion. Option D is wrong because H2SO4 is sulphuric acid itself, a compound that releases hydrogen ions in water. Exam tip: acids give H3O+ ions in water and bases give OH- ions; a solution with pH 7 is neutral, below 7 acidic and above 7 basic.

The correct answer is A, The pressure in blood vessels exceeds outside pressure. At great heights the air is thin, so the atmospheric pressure acting on the body is much lower than at sea level. The blood inside our vessels keeps pushing outwards at nearly its usual pressure. In the nose the blood vessels are very fine and lie close to the surface, so when the pressure inside them becomes greater than the pressure outside, some of them burst and the nose bleeds. The cold, dry mountain air also makes the lining of the nose crack more easily. The same fall in air pressure is why water boils below 100 °C on mountains and food takes longer to cook. B is wrong because the pressure inside the vessels becomes more than, not less than, the outside pressure. C is wrong because equal pressures would give no push to burst the vessels. D is wrong because blood does not become thick enough at a height to cause nose bleeding. Exam tip: higher altitude, lower air pressure, so the pressure in blood vessels is relatively higher and the nose can bleed.

The correct answer is A, Bauxite, Magnetite, Malachite and Calamine respectively. Each metal here is paired with one of its best-known ores. Bauxite is hydrated aluminium oxide; alumina is refined from it and then broken down by electrolysis in the Hall-Héroult process. Magnetite (Fe3O4) is the magnetic ore of iron, while haematite (Fe2O3) is India's chief iron ore. Malachite is a green basic copper carbonate, though copper pyrites is the main commercial ore of copper. Calamine is zinc carbonate (ZnCO3), and zinc blende (ZnS) is the other main ore of zinc; the Zawar mines of Rajasthan are famous for it. Option B is wrong because it gives aluminium to magnetite and iron to bauxite. Option C is wrong because it runs the list backwards, pairing aluminium with calamine and zinc with bauxite. Option D is wrong because malachite is an ore of copper, not aluminium, and bauxite is not an ore of copper. Exam tip: "B-M-M-C" in order: Bauxite-Al, Magnetite-Fe, Malachite-Cu, Calamine-Zn.

The correct answer is C, 277. Water is densest at about 4 degrees Celsius, and 4 plus 273 gives roughly 277 kelvin. Most liquids keep shrinking as they cool, but water behaves oddly: below 4 degrees Celsius it starts to expand again because its molecules begin forming the open, hexagonal pattern of ice. This anomalous expansion is why ice is lighter than water and floats, and why a lake freezes from the top while the 4-degree water sinks to the bottom, letting fish survive the winter. Its density at that point is very close to 1 gram per cubic centimetre. D is wrong because 273 kelvin is 0 degrees Celsius, the freezing point, where water is already less dense than at 4 degrees. A is wrong because 0 kelvin is absolute zero, where no liquid water can exist. B is wrong because 227 kelvin is about minus 46 degrees Celsius, far below freezing. Exam tip: maximum density of water at 4 degrees Celsius equals 277 K; freezing at 273 K, boiling at 373 K.

The correct answer is B, Chlorine. Bleaching powder gives off chlorine when it reacts with water, and this chlorine does the bleaching and kills germs. Bleaching powder is calcium oxychloride, CaOCl2, made by passing chlorine gas over dry slaked lime, Ca(OH)2. With water it gives back calcium hydroxide and chlorine: CaOCl2 + H2O → Ca(OH)2 + Cl2. The chlorine it can release is called "available chlorine", which is why the powder smells of chlorine and is used to disinfect drinking water and swimming pools and to bleach cotton and paper. A is wrong because bleaching powder does not give off hydrogen gas. C is wrong because carbon monoxide comes from the incomplete burning of fuels. D is wrong because carbon dioxide is released when an acid reacts with a carbonate such as washing soda or baking soda. Exam tip: Bleaching powder = CaOCl2 (releases chlorine), Baking soda = NaHCO3, Washing soda = Na2CO3.10H2O, Plaster of Paris = CaSO4.½H2O.

The correct answer is A, 20 Hz – 20000 Hz. A healthy human ear can hear sound waves with frequencies from about 20 hertz to 20,000 hertz (20 kHz); this band is called the audible range. Sounds below 20 Hz are called infrasonic, and animals such as elephants and whales use them to communicate over long distances. Sounds above 20 kHz are called ultrasonic; bats, dogs and dolphins can hear them, and ultrasound is used in medical scans, in cleaning delicate parts and in SONAR. Children under five and some animals can hear up to about 25 kHz, and the upper limit falls as people grow older. Option B is wrong because 80 to 100 Hz is only a tiny slice of the audible range. Option C is wrong because 2 lakh to 4 lakh Hz, that is 200 to 400 kHz, lies far inside the ultrasonic range. Option D is wrong because 0 to 20 Hz is the infrasonic range, which humans cannot hear. Exam tip: infrasonic below 20 Hz, audible from 20 Hz to 20 kHz, ultrasonic above 20 kHz.

The correct answer is B, Pulmonary vein. Veins usually carry blood low in oxygen back to the heart, but the pulmonary veins are the exception. After blood picks up oxygen in the lungs, four pulmonary veins, two from each lung, bring this oxygen-rich blood to the left atrium of the heart. From there it passes to the left ventricle, which pumps it to the whole body through the aorta. The mirror-image fact is asked just as often: the pulmonary artery is the only artery that carries deoxygenated blood, taking it from the right ventricle to the lungs. So the rule is that arteries carry blood away from the heart and veins carry it towards the heart, whatever its oxygen level. Option A is wrong because the cystic vein drains the gall bladder. Option C is wrong because the hepatic portal vein carries nutrient-rich but oxygen-poor blood from the intestines to the liver. Option D is wrong because the cardiac veins drain used blood from the heart muscle into the right atrium. Exam tip: pulmonary vein, the only vein with oxygenated blood; pulmonary artery, the only artery with deoxygenated blood.

The correct answer is B, Adrenal gland. Adrenaline is made by the adrenal glands, which sit like caps on top of the two kidneys. It is released in fear, anger or sudden danger, so it is called the "fight or flight" hormone. It raises the heartbeat and breathing rate, increases blood sugar and sends more blood to the muscles so that the body can react fast. Adrenaline comes from the inner part of the gland, the adrenal medulla; the outer part, the cortex, makes cortisol and aldosterone. A is wrong because the thyroid gland in the neck makes thyroxine, which controls metabolism and needs iodine. C is wrong because the pineal gland in the brain makes melatonin, which controls the sleep-wake cycle. D is wrong because the pituitary gland makes growth hormone and controls several other glands, so it is called the master gland. Exam tip: Adrenal = adrenaline (emergency hormone), Thyroid = thyroxine (metabolism), Pancreas = insulin (blood sugar), Pituitary = master gland.

The correct answer is A, B3. Pellagra is caused by a lack of vitamin B3, also called niacin or nicotinic acid. The body can also make niacin from the amino acid tryptophan, so the disease is common where people live mainly on maize, which is poor in both. Pellagra is remembered by the 'four Ds': dermatitis (rough, dark skin on parts exposed to the sun), diarrhoea, dementia and, if untreated, death. Niacin is found in meat, fish, groundnuts, whole grains and milk. B is wrong because vitamin B6 (pyridoxine) deficiency causes anaemia, skin problems and convulsions in infants. C is wrong because vitamin B2 (riboflavin) deficiency causes cracked lips and sores at the corners of the mouth, called ariboflavinosis. D is wrong because vitamin B12 (cobalamin) deficiency causes pernicious anaemia and nerve damage. Exam tip: B1 beriberi, B2 ariboflavinosis, B3 pellagra, B12 pernicious anaemia; pellagra = the four Ds.

The correct answer is B, Falciparum. Plasmodium falciparum causes malignant, or cerebral, malaria, the most dangerous form of the disease. Red blood cells infected by it become sticky and block the small blood vessels of the brain and other organs, which can lead to coma and death if treatment is delayed. Malaria spreads through the bite of the female Anopheles mosquito; the parasite first multiplies in the liver and then in red blood cells, and the bursting of these cells brings the cycles of chills and high fever. Ronald Ross proved the mosquito link in 1897 while working in India and won the Nobel Prize in 1902. Option A is wrong because P. vivax causes benign tertian malaria, which can relapse from dormant stages in the liver but is rarely fatal. Option C is wrong because P. ovale causes a mild tertian malaria found mainly in Africa. Option D is wrong because P. malariae causes quartan malaria, with fever every fourth day. Exam tip: falciparum = malignant; vivax = benign but relapsing; female Anopheles = vector.