General Science Mixed Quiz: Set 13

The correct answer is C, 27 K. A rise of 27°C is a rise of 27 K, because one degree Celsius and one kelvin are exactly the same size. The two scales differ only in where they begin: the melting point of ice is 0°C but 273.15 K. So the formula T(K) = t(°C) + 273.15 converts a reading, not a difference. When two temperatures are subtracted the 273.15 cancels out, which is why a rise, a fall or an interval carries the same number on both scales. Option D, 300 K, is the trap in this question: 27 + 273 is the Kelvin reading of a body that is at 27°C, not the size of a 27-degree rise. Options A and B follow from no step at all; they would need a scale whose divisions are smaller than the Celsius degree, and the kelvin is not such a unit. Exam tip: add 273.15 to a reading, but copy an interval straight across.

The correct answer is A, Archimedes' Principle. It states that the upthrust on a body dipped fully or partly in a fluid equals the weight of the fluid the body pushes aside. This is why a bucket of water feels lighter while it is still in the well, and why a ship of steel floats: its hollow shape displaces enough water to balance its own weight. The principle also gives the law of flotation and is used to find the purity of metals and the density of liquids with a hydrometer. B is wrong because Bernoulli's principle links the speed of a flowing fluid with its pressure, and explains lift on an aeroplane wing. C is wrong because the Beer–Lambert law deals with how much light a solution absorbs as it passes through. D is wrong because Pascal's law says pressure applied to an enclosed fluid is passed on equally in every direction, which is the basis of hydraulic brakes and lifts. Exam tip: Archimedes for buoyancy, Pascal for hydraulic press, Bernoulli for aerofoil lift.

The correct answer is A, 6.67 m/s². Find each mass from F = ma, add the masses, then divide the same force by the total. The first block gives m1 = 5 ÷ 10 = 0.5 kg and the second gives m2 = 5 ÷ 20 = 0.25 kg. Tied together they move as one body of mass 0.5 + 0.25 = 0.75 kg, and the same 5 N force now produces an acceleration of 5 ÷ 0.75, which is about 6.67 m/s². The joint acceleration is always less than the smaller of the two single accelerations, because the same push has to move more mass. Option B is wrong because 1.67 m/s² matches no step of this working. Option C is wrong because 5.67 m/s² would need a total mass of about 0.88 kg. Option D is wrong because 4.67 m/s² would need a total mass of about 1.07 kg. Exam tip: for one force on tied blocks the reciprocals add, that is 1 by a equals 1 by a1 plus 1 by a2.

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 D, 75%. The ball falls from 10 m but rises back only 2.5 m, so it keeps one quarter of its energy and loses three quarters. Just before the ball hits the ground, its kinetic energy equals the potential energy it had at the top, that is mgh with h = 10 m. Just after the bounce, the kinetic energy is only as much as is needed to lift it 2.5 m, so it is mg multiplied by 2.5. The ratio is 2.5 divided by 10, which is one fourth, so 25 per cent of the kinetic energy is left and 75 per cent is lost as heat and sound during the collision. The mass cancels out, so the heights alone decide the answer. Option A is wrong because the ball does rebound, so all the energy is not lost. Option B is wrong because 25 per cent is the energy kept, not the energy lost. Option C is wrong because losing half the energy would take the ball back to 5 m. Exam tip: in a bounce, percentage loss equals (1 minus h2 by h1) multiplied by 100.

The correct answer is C, Calcium oxychloride. Calcium oxychloride (CaOCl2) is bleaching powder, and the chlorine it releases removes colour from cotton and linen in the textile industry. It is made by passing chlorine gas over dry slaked lime, Ca(OH)2. When it reacts with water or a dilute acid it gives out chlorine, and this chlorine oxidises the colouring matter into colourless substances. Bleaching powder is also used to bleach wood pulp in paper mills and to disinfect drinking water, which is why it smells of chlorine. A is wrong because sodium carbonate is washing soda, used to remove the permanent hardness of water and in making glass. B is wrong because sodium hydrogencarbonate is baking soda, used in cooking and as an antacid. D is wrong because calcium chloride is a drying agent that absorbs moisture, not a bleach. Exam tip: bleaching powder CaOCl2, washing soda Na2CO3·10H2O, baking soda NaHCO3.

The correct answer is B, Pascal. Pressure is thrust per unit area, so its unit is one newton per square metre, and this unit is named the pascal after Blaise Pascal. Atmospheric pressure at sea level is about one hundred and one thousand pascals, and the commercial unit bar equals one hundred thousand pascals.

Option A, the newton, is the SI unit of force itself, not of force spread over an area, and it is the numerator in the definition of pressure. Option C, the joule, is the unit of work and energy and equals a newton metre, which is a force multiplied by a distance rather than divided by an area. Option D, the watt, is the unit of power and equals one joule per second. Learn the four together because papers frequently ask which unit goes with which quantity, and pascal, newton, joule and watt appear in the same option set.

The correct answer is C, Red blood cells. Mature red blood cells, or erythrocytes, lose their nucleus before they enter the blood. Losing the nucleus, and the mitochondria too, leaves more room for haemoglobin, the iron-rich protein that carries oxygen, and gives the cell its flexible biconcave disc shape, which lets it squeeze through narrow capillaries. With no nucleus, red blood cells cannot divide or repair themselves; they live about 120 days, are made in the red bone marrow and are broken down mainly in the spleen, often called the graveyard of red blood cells. Platelets also lack a nucleus, but they are cell fragments, not whole cells. A is wrong, because muscle cells have nuclei, and skeletal muscle fibres even have many. B is wrong, because phagocytic cells such as neutrophils and macrophages have a nucleus; a neutrophil's nucleus has several lobes. D is wrong, because the ciliated cells lining the windpipe and the oviduct are normal cells with a nucleus. Exam tip: human red blood cells have no nucleus, live 120 days, are born in bone marrow and end in the spleen.

The correct answer is B, the joule. Heat is a form of energy in transit, so it is measured in the same unit as work and energy, the joule, which is one newton metre.

Option A, the calorie, is an older and still familiar unit of heat, defined as the heat needed to raise the temperature of one gram of water by one degree Celsius; it equals about 4.2 joules, but it is not the SI unit. Option C, the kelvin, is the SI unit of temperature, not of heat, and the difference between heat and temperature is exactly what this question tests. Option D, the watt, is the unit of power, that is the rate of doing work or of transferring energy, one joule per second, so a heater rated in watts tells you how fast it supplies heat, not how much.

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 C, remains same. Loudness and frequency are two different properties of sound. Loudness depends on the amplitude of the vibration, that is how far the vibrating part moves from its rest position, while frequency is the number of vibrations made in one second and is measured in hertz. Turning the volume up makes the speaker push the air harder, so the amplitude and therefore the loudness rise, but the tune still plays the same notes, so the frequency does not change. This is why the ringtone sounds stronger and not higher in pitch. A and B are wrong because a change in frequency would change the pitch, and a louder ringtone would then sound shriller or deeper, which does not happen. D is wrong because the relation is definite and well known, so it can certainly be decided. Exam tip: amplitude decides loudness, frequency decides pitch, and the speed of sound in air depends only on the medium.

The correct answer is D, Bowman's capsule. Each human kidney has about one million nephrons, and every nephron begins with a cup-shaped Bowman's capsule that encloses a knot of capillaries called the glomerulus. Blood enters the glomerulus under pressure, and water, salts, glucose, urea and other small molecules are pushed out through its walls into the capsule; this is ultrafiltration, the first step of urine formation. Proteins and blood cells are too large to pass and stay in the blood. The filtrate then flows through the tubule, where useful substances such as glucose and most of the water are reabsorbed. A, the Collecting duct, only gathers urine from many nephrons and carries it to the pelvis of the kidney. B, the Renal vein, carries filtered blood away from the kidney and is not part of a nephron. C, the Ureter, is the tube that takes urine from the kidney to the bladder. Exam tip: Bowman's capsule plus glomerulus is the Malpighian body, the filter of the nephron.

The correct answer is B. Potential difference between two points of a circuit is the difference in electric potential between them, and it equals the work done in moving a unit positive charge from one point to the other. In symbols V = W/Q, so the unit is the volt, and one volt means one joule of work for each coulomb of charge. Potential difference is the push that drives a current, it is measured with a voltmeter joined in parallel across the two points, and Ohm's law links it to current as V = IR. Option A is wrong because capacitance is the charge a capacitor stores for each volt applied, measured in farad; it is a property of the device, not a difference between points. Option C is wrong because current is the rate of flow of charge, measured in ampere by an ammeter placed in series, and in a series circuit it is the same everywhere. Option D is wrong because resistance opposes current and is measured in ohm. Exam tip: V = W/Q, voltmeter in parallel, ammeter in series.

The correct answer is D, Medulla. The medulla oblongata is the breathing centre of the brain, which is why we keep breathing even while asleep. It is the lowest part of the hindbrain and joins the brain to the spinal cord. It controls involuntary actions such as breathing, heartbeat, blood pressure, swallowing, coughing, sneezing and vomiting. It senses the level of carbon dioxide in the blood and speeds up or slows down breathing to match, so an injury at the base of the skull can be fatal. A is wrong because the forebrain (cerebrum) handles thinking, memory, speech and voluntary actions. B is wrong because the cerebellum keeps the body balanced and makes voluntary movements smooth and precise. C is wrong because the midbrain mainly carries reflexes linked to seeing and hearing. Exam tip: Medulla = breathing and heartbeat, Cerebellum = balance, Cerebrum = thinking and memory, Hypothalamus = body temperature, hunger and thirst.

The correct answer is D, Argon. Argon is a noble gas whose outer shell already holds eight electrons, so it has no room to take another one easily; adding an electron would mean starting a new shell, and energy has to be supplied rather than released. Its electron affinity is therefore effectively zero, the lowest of the four. Electron affinity is the energy change when a neutral gaseous atom gains an electron, and it generally rises across a period and falls down a group. The other three are halogens, one electron short of a stable octet, so they release a lot of energy on gaining an electron. Option A is wrong because fluorine has a very high electron affinity, though its small size and crowded electrons push it just below chlorine. Option B is wrong because chlorine has the highest electron affinity of all elements. Option C is wrong because bromine's affinity, while lower than chlorine's, is still far above argon's. Exam tip: order is Cl greater than F greater than Br greater than I, and noble gases sit at the bottom.

The correct answer is A, Protein. The lens of the eye is made mostly of water and special proteins called crystallins, packed in a very regular order that keeps the lens clear so light can pass straight through to the retina. With age, and faster with diabetes, ultraviolet light, smoking or an injury, these proteins break down and clump together. The clumps scatter light, so the lens turns cloudy and vision becomes blurred, dim and glary. This clouding is a cataract, and it is one of the leading causes of blindness in India. It is treated by a short operation in which the cloudy lens is removed and replaced by an artificial intraocular lens. Option B is wrong because carbohydrate changes are not what clouds the lens, although high blood sugar in diabetes speeds up the protein damage. Option C is wrong because fat does not form the clear structure of the lens. Option D is wrong because the tear glands keep the eye moist and have nothing to do with the lens. Exam tip: cataract = cloudy lens from clumped proteins; glaucoma = raised pressure inside the eye.

The correct answer is D, Intermolecular forces are weak. Melting and boiling only have to break the weak forces between the molecules, not the strong bonds inside them, so little heat is needed.

A covalent bond is formed by the sharing of electrons and is itself strong, but it acts only within the molecule. Separate molecules are held to one another by weak van der Waals forces, and these give way at low temperature, which is why water, ammonia, carbon dioxide and most organic compounds melt and boil easily. Ionic compounds such as sodium chloride behave in the opposite way: a strong electrostatic force runs through the whole crystal, so their melting points are very high. Giant covalent solids like diamond and silicon carbide are the exception, since their bonds form a continuous network.

Options A, B and C are wrong because they all claim the forces between molecules are medium or strong, which would raise the melting and boiling points instead of lowering them.

Exam tip: strong bond inside the molecule, weak force between molecules, so covalent compounds melt at low temperature.

The correct answer is B, sulphurous acid. Sulphur dioxide dissolves in water to give sulphurous acid, a weak acid with the formula H2SO3, by the reaction SO2 + H2O to H2SO3. Sulphur dioxide is an oxide of a non-metal, and such oxides are acidic in nature, which is why the solution turns blue litmus red. The same gas, released when coal and diesel burn, dissolves in rain water in the air and is then slowly oxidised further, so sulphur dioxide is one of the main causes of acid rain. A is wrong because sulphur trioxide is made by oxidising sulphur dioxide with more oxygen over a catalyst, not by dissolving it in water. C is wrong because sulphuric acid is formed when sulphur trioxide, and not sulphur dioxide, meets water. D is wrong because sulphur is the element itself and cannot be got back simply by dissolving its oxide. Exam tip: SO2 with water gives H2SO3; SO3 with water gives H2SO4.

The correct answer is C, Silver. Silver is a noble metal and does not combine with oxygen even when it is heated strongly. Metals react with oxygen according to their place in the reactivity series. Very reactive metals such as potassium and sodium burn in air at room temperature, aluminium and zinc form an oxide layer when heated, and lead slowly turns into lead oxide on heating. Silver, gold and platinum lie at the bottom of the series, so they keep their shine in air; the black film that appears on silverware is silver sulphide formed by sulphur gases, not silver oxide. Option A is wrong because zinc burns with a bluish white flame and gives zinc oxide. Option B is wrong because aluminium forms a thin, tough coat of aluminium oxide that protects the metal below it. Option D is wrong because lead heated in air gives litharge, which is lead oxide. Exam tip: gold, silver and platinum are the noble metals that resist oxidation, which is why they are used in jewellery and contacts.

The correct answer is D, Bryophytes. Moss, or Funaria, and Marchantia, a liverwort, are bryophytes, the group called the amphibians of the plant kingdom because they live on land but need water for reproduction. Bryophytes have no true roots, stems or leaves and no vascular tissue, so they stay small and grow in damp, shady places; they cling to the soil with thread-like rhizoids and their male gametes swim to the female in a film of water. Mosses help to hold soil and prevent erosion, and Sphagnum moss gives peat. Option A is wrong because algae are simple, mostly aquatic thallophytes such as Spirogyra and Chara. Option B is wrong because gymnosperms are seed plants with naked seeds, such as pine, cycas and deodar. Option C is wrong because pteridophytes, such as ferns and Selaginella, have vascular tissue but no seeds. Exam tip: thallophyta means algae, bryophyta means mosses and liverworts, pteridophyta means ferns, and the seed plants are gymnosperms and angiosperms.