General Science Mixed Quiz: Set 9

The correct answer is B, lactometer. A lactometer floats in milk and shows its relative density. Pure milk is denser than water, so adding water lowers the density and the instrument sinks deeper, which reveals the adulteration. It is in effect a hydrometer calibrated for one particular liquid.

Option A, the hydrometer, measures the relative density of liquids in general, so it is the parent instrument rather than the specific answer this question wants. Option C, the pyrometer, measures very high temperatures, such as those inside a furnace, without touching the hot body. Option D, the fathometer, measures the depth of the sea using sound waves. Instrument questions are pure pairing questions, so revise them as a table rather than one at a time. A lactometer is therefore read where its stem meets the surface of the milk, and a reading below the pure-milk mark points to added water.

The correct answer is B, Quantum Computing. A qubit, short for quantum bit, is the basic unit of information in a quantum computer. An ordinary bit can be only 0 or 1, but a qubit can exist in a superposition of 0 and 1 at the same time, and qubits can be entangled, so that the state of one is linked to another. Because of this, a set of qubits can explore many possibilities together, which could let quantum computers solve certain problems, such as simulating molecules or breaking some kinds of encryption, far faster than classical machines. Qubits are built from superconducting circuits, trapped ions or photons, and most must be kept close to absolute zero. India supports this field through its National Quantum Mission, approved in 2023. Option A is wrong because cloud services run on ordinary bits and servers. Option C is wrong because visible light communication, or Li-Fi, sends data using LED light. Option D is wrong because wireless communication uses radio waves, not qubits. Exam tip: a bit is 0 or 1, a qubit means superposition and entanglement.

The correct answer is C, Vitamin C. Milk contains very little vitamin C, and what little there is gets destroyed further when milk is boiled. Milk is otherwise called a nearly complete food: it gives calcium and phosphorus for bones and teeth, good-quality protein, mainly casein, the sugar lactose, fat, and vitamins A, B2 and B12. Its two well-known gaps are vitamin C and iron. Vitamin C, or ascorbic acid, comes from fresh fruits such as amla, guava, lemon and orange, and a lack of it causes scurvy, with bleeding gums as the classic sign. Option A is wrong because milk is one of the richest everyday sources of calcium. Option B is wrong because milk supplies good protein, which is why it is advised for growing children. Option D is wrong because milk carries a carbohydrate of its own, lactose, the milk sugar. Exam tip: milk is poor in vitamin C and iron, and rich in calcium, protein and lactose.

The correct answer is C, Newtonian telescope. Isaac Newton built the first practical reflecting telescope in 1668. In it, light from the star falls on a large concave mirror at the bottom of the tube, and a small flat mirror set at 45 degrees near the top turns the light sideways to the eyepiece. Because the objective is a mirror and not a lens, there is no chromatic aberration, the colour fringing that lenses produce, and a mirror can be made much larger and lighter than a lens. Most big observatory telescopes are therefore reflectors. A, the Galilean telescope, is a refractor using a convex objective lens and a concave eyepiece lens. B, the Keplerian telescope, is also a refractor, with two convex lenses, and gives an inverted image. D, the Schmidt telescope, is a catadioptric design that combines a spherical mirror with a glass corrector plate, so it is not mirrors only. Exam tip: refractor means lenses (Galileo, Kepler), reflector means mirrors (Newton), Schmidt means a mirror plus a corrector lens.

The correct answer is C, Stapedius. The stapedius, only about 1 millimetre long, is the smallest skeletal muscle in the human body. It lies in the middle ear and is attached to the stapes, which is itself the smallest bone of the body. When a very loud sound reaches the ear, the stapedius contracts and damps the vibration of the stapes, protecting the delicate inner ear; this is called the acoustic reflex. It is supplied by the facial nerve, so damage to that nerve can make ordinary sounds seem painfully loud. Option A is wrong because the biceps is a large muscle at the front of the upper arm that bends the elbow. Option B is wrong because the sartorius, which runs across the thigh, is the longest muscle of the body, not the smallest. Option D is wrong because the triceps at the back of the upper arm straightens the elbow and is a large muscle. Exam tip: smallest muscle stapedius, smallest bone stapes, longest muscle sartorius, largest muscle gluteus maximus.

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 B, Pressure. The torr is a unit of pressure named after Evangelista Torricelli, the Italian scientist who invented the mercury barometer in 1643. One torr is the pressure of a one-millimetre column of mercury, so 1 torr = 1 mm Hg, and it equals about 133.3 pascal. Normal atmospheric pressure at sea level is 760 torr, which is the same as 760 mm Hg, 1 atmosphere or 101,325 pascal. The pascal is the SI unit of pressure, one newton per square metre, but the torr and mm Hg are still used for blood pressure and vacuum work. A, Power, is measured in watt, with horsepower as the older unit. C, Energy, is measured in joule, with calorie and electron-volt as other units. D, Force, is measured in newton, or dyne in the CGS system. Exam tip: pressure units are pascal, bar, atmosphere, torr and mm Hg; 760 torr = 1 atm.

The correct answer is C, AB+. A person with AB positive blood can receive red cells from every ABO and Rh group, so AB+ is called the universal recipient. The reason is simple: AB+ red cells carry the A antigen, the B antigen and the Rh (D) antigen, so the plasma has no anti-A, anti-B or anti-Rh antibodies to attack donated blood. The opposite case is O negative, whose red cells have none of these antigens, which makes O− the universal donor. Karl Landsteiner discovered the ABO groups in 1900 and received the Nobel Prize in 1930. A is wrong because O+ plasma has both anti-A and anti-B antibodies, so it accepts only O blood. B is wrong because A+ has anti-B antibodies and cannot take B or AB blood. D is wrong because B+ has anti-A antibodies and cannot take A or AB blood. Exam tip: AB+ receives from all, O− gives to all.

The correct answer is B, Vitamin K. The liver needs vitamin K to make prothrombin and other clotting factors, so without it blood takes much longer to clot. The letter K comes from the German word Koagulation, which makes it easy to remember. Vitamin K1, or phylloquinone, comes from green leafy vegetables such as spinach, and bacteria in the large intestine also make a form of it. Newborn babies have very little vitamin K, which is why they are given a vitamin K injection at birth to prevent bleeding. A lack of it causes easy bruising and bleeding that does not stop. Option A is wrong because vitamin A, retinol, is needed for vision, and its lack causes night blindness. Option C is wrong because vitamin D, calciferol, helps absorb calcium, and its lack causes rickets. Option D is wrong because the B vitamins help release energy from food, and their lack causes diseases such as beriberi and pernicious anaemia. Exam tip: K for Koagulation; A for eyes, D for bones.

The correct answer is C, Insulin. The pancreas is both an exocrine gland, pouring digestive enzymes into the intestine, and an endocrine gland. Its endocrine part is made of small clusters of cells called the islets of Langerhans. The beta cells in these islets release insulin, which lowers blood sugar by helping body cells take in glucose and by making the liver store extra glucose as glycogen. When the body makes too little insulin, or cannot use it properly, blood sugar stays high, which is diabetes mellitus. Insulin was discovered in 1921 by Frederick Banting and Charles Best. Option A is wrong because adrenaline, the ‘fight or flight’ hormone, comes from the medulla of the adrenal gland. Option B is wrong because glucagon is made by the alpha cells of the same islets, and it raises blood sugar, the opposite of insulin. Option D is wrong because aldosterone comes from the adrenal cortex and helps the kidneys keep back sodium and water. Exam tip: alpha cells make glucagon and raise sugar; beta cells make insulin and lower it.

The correct answer is D, [M L T⁻²]. Newton's second law gives force = mass × acceleration. Mass has the dimension [M], and acceleration is velocity divided by time, that is [L T⁻¹] ÷ [T] = [L T⁻²]. Multiplying, force = [M L T⁻²]. Its SI unit is the newton, 1 N = 1 kg m s⁻², and its CGS unit is the dyne, with 1 N = 10⁵ dyne. Weight, tension, thrust and friction are all forces, so they share the same dimensional formula, which is a favourite exam trick. Option A is wrong because [M⁰ L³ T⁰] is simply [L³], the dimension of volume. Option B is wrong because [M L⁻³ T⁰] is mass per unit volume, that is density. Option C is wrong because [M⁰ L T⁻¹] is length per unit time, the dimension of speed or velocity. Exam tip: build from the definition: velocity [L T⁻¹], acceleration [L T⁻²], force [M L T⁻²], work and energy [M L² T⁻²], power [M L² T⁻³], pressure [M L⁻¹ T⁻²].

The correct answer is C, Thymine. In DNA, adenine always pairs with thymine through two hydrogen bonds, and guanine pairs with cytosine through three. This is called complementary base pairing, and it is why one strand of DNA can be used to copy the other. The double-helix model was proposed by James Watson and Francis Crick in 1953, using X-ray images made by Rosalind Franklin. Adenine and guanine are purines with two rings, while thymine and cytosine are pyrimidines with one ring, so each pair has the same width and the helix stays even. In RNA, thymine is replaced by uracil. Option A is wrong because guanine is a purine like adenine and pairs with cytosine. Option B is wrong because cytosine pairs with guanine through three hydrogen bonds. Option D is wrong because histone is a protein around which DNA is wound in chromosomes; it is not a base at all. Exam tip: A pairs with T by two bonds, G with C by three; RNA has U in place of T.

The correct answer is A, Vitamin K. The liver needs vitamin K to make several clotting factors, including prothrombin, which help blood form a clot and seal a wound. Its letter comes from the German word ‘Koagulation’. When it is lacking, even small cuts bleed for a long time and bruises form easily. Newborn babies have very little of it, so hospitals give them a vitamin K injection at birth to prevent dangerous bleeding. Good sources are green leafy vegetables such as spinach, cabbage and fenugreek, and bacteria in our gut also make some of it. It is a fat-soluble vitamin, like A, D and E. Option B is wrong because vitamin E (tocopherol) works mainly as an antioxidant that protects cells. Option C is wrong because vitamin A (retinol) is needed for vision, and its lack causes night blindness. Option D is wrong because vitamin C (ascorbic acid) keeps gums and skin healthy; its lack causes scurvy, with bleeding gums, but it is not a clotting vitamin. Exam tip: K for Koagulation; A for night blindness, C for scurvy, D for rickets.

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 C, Pascal. Pressure is force acting per unit area, so its SI unit is the newton per square metre, which is given the special name pascal (Pa) after the French scientist Blaise Pascal, who stated the law of transmission of pressure in liquids used in hydraulic brakes and lifts. One pascal is a very small pressure, so larger units are common: 1 bar = 10⁵ Pa, 1 atmosphere = 101,325 Pa = 760 mm of mercury, and weather reports use the hectopascal (1 hPa = 100 Pa), while blood pressure is still read in mm Hg. Option A is wrong because the volt is the SI unit of electric potential difference (1 V = 1 J/C). Option B is wrong because the ampere is the SI base unit of electric current. Option D is wrong because the ohm is the SI unit of electrical resistance (1 Ω = 1 V/A). Exam tip: pressure = force ÷ area, N/m² = pascal; and the electrical trio: volt for voltage, ampere for current, ohm for resistance.

The correct answer is C, 1 and 3 only. The cooking temperature is set by the pressure inside the cooker, and that pressure is fixed by the weight sitting on the vent and the area of the hole under it. The boiling point of water rises with pressure. In an open pan water boils at 100°C, but when steam is trapped, pressure builds up until it can lift the weight, the whistle, off the vent. Pressure is force divided by area, so a heavier weight or a smaller hole means a higher pressure before steam escapes, and water then boils at about 120°C, which is why food cooks faster. Statement 2 is wrong because a bigger flame only makes the water boil and the whistle blow sooner; once steam escapes, the temperature stays at the boiling point for that pressure, and extra heat just makes more steam. Statements 1 and 3 are right for the reason above. So options A, B and D, which include statement 2, are wrong. Exam tip: higher pressure means a higher boiling point; the flame changes the speed, not the temperature.

The correct answer is D, Vitamin K. Vitamin K is needed to make the clotting proteins, so without it even a small cut keeps bleeding. The liver uses vitamin K to make prothrombin and other clotting factors that turn blood into a clot at a wound. The letter K comes from the German word "Koagulation", meaning clotting. Green leafy vegetables such as spinach and cabbage are rich sources, and bacteria in the large intestine also make some of it. Newborn babies are usually given a vitamin K injection because they are born with very little. A is wrong because lack of the vitamin B group causes diseases like beriberi (B1) and pellagra (B3). B is wrong because lack of vitamin A causes night blindness. C is wrong because lack of vitamin C causes scurvy with bleeding gums, but the vitamin that makes blood clot is K. Exam tip: A = night blindness, B1 = beriberi, C = scurvy, D = rickets, K = bleeding; vitamins A, D, E and K dissolve in fat.

The correct answer is A, Candela. Luminous intensity is the amount of visible light a source sends out in a given direction per unit solid angle, and its SI base unit is the candela (cd), roughly the light of one ordinary candle. It is one of the seven SI base units: metre for length, kilogram for mass, second for time, ampere for electric current, kelvin for temperature, mole for amount of substance and candela for luminous intensity. Do not mix it up with the lumen, the unit of luminous flux (total light output), or the lux, the unit of illuminance (lumens per square metre falling on a surface). Option B is wrong because the mole measures amount of substance, 6.022 × 10²³ particles. Option C is wrong because the kelvin measures thermodynamic temperature. Option D is wrong because the ampere measures electric current. Exam tip: the seven base units in one line: m, kg, s, A, K, mol, cd; candela = intensity, lumen = flux, lux = illuminance.

The correct answer is D, A and D. Vitamins A, D, E and K dissolve in fat, while the B group and vitamin C dissolve in water. Fat-soluble vitamins are absorbed along with the fat in our food and are stored in the liver and fatty tissue, so the body can build up a reserve; for the same reason, too much of them, especially A and D taken as supplements, can be harmful. Most water-soluble vitamins are not stored in large amounts, the extra is passed out in urine, and so they must be eaten regularly. Vitamin A keeps the eyes healthy and its lack causes night blindness, while vitamin D is made in the skin in sunlight and its lack causes rickets in children. Option A is wrong because vitamin B12 is water-soluble, even though D is fat-soluble. Option B is wrong because vitamin C is water-soluble. Option C is wrong because it pairs fat-soluble A with water-soluble C. Exam tip: remember the fat-soluble group as 'ADEK'; the B group and C are water-soluble.

The correct answer is B, A = 1C/s. One ampere is the current that flows when one coulomb of charge passes a point in a circuit in one second. It comes straight from the formula I = Q/t, where I is current in amperes, Q is charge in coulombs and t is time in seconds. The ampere is one of the seven SI base units and is named after the French physicist André-Marie Ampère. One coulomb is the charge of roughly 6.25 × 10¹⁸ electrons, so a current of 1 ampere means that many electrons flowing past a point every second. Turned around, the same formula gives Q = I × t, which is why a coulomb is also called an ampere-second. A is wrong because 2 coulombs per second is a current of 2 amperes, not 1. C is wrong because charge is current multiplied by time, not current divided by time. D is wrong because an ampere multiplied by 2 seconds gives 2 coulombs, not the definition of 1 ampere. Exam tip: I = Q/t, so 1 A = 1 C/s and 1 C = 1 A × 1 s.