General Science Mixed Quiz: Set 3

The correct answer is C, newton. The newton is a derived unit: it is built from the kilogram, the metre and the second, since force equals mass times acceleration, and it can be written as one kilogram metre per second squared. Derived units are always expressible in terms of the base units.

Option A, the kelvin, is the base unit of thermodynamic temperature. Option B, the mole, is the base unit for the amount of substance and contains as many entities as there are atoms in a fixed quantity of carbon-12 under the older definition. Option D, the candela, is the base unit of luminous intensity and is the one most often forgotten in the list. In this style of question the odd one out is almost always a unit named after a scientist, such as the newton, joule, watt, pascal or hertz.

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, un-deviated. A ray that passes through the optical centre of a thin lens comes out in the same direction, without any bending. The optical centre is the central point of the lens on its principal axis. Near it the two faces of the lens are almost parallel, like a thin glass slab, so the ray shifts sideways by a negligible amount and keeps its direction. This is one of the three standard rays used to draw ray diagrams: a ray parallel to the principal axis passes through the focus after refraction in a convex lens, a ray through the focus comes out parallel to the axis, and a ray through the optical centre goes straight on. B is wrong because only rays that strike the lens away from the centre are deviated. C is wrong because bent means the same as deviated, which does not happen at the centre. D is wrong because a lens refracts light; reflection is what mirrors do. Exam tip: through the optical centre = straight through; parallel ray = through the focus; ray through the focus = emerges parallel.

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 D, Fleming's Left-Hand Rule. It gives the direction of the force, and so of the motion, on a current-carrying conductor placed in a magnetic field, which is exactly what turns the coil of a motor. Stretch the thumb, forefinger and middle finger of the left hand so that they are at right angles to one another. If the forefinger points along the magnetic field and the middle finger along the current, the thumb points in the direction of the force. The force is greatest when the current is at right angles to the field. A is wrong because Ampere's law relates the magnetic field around a closed loop to the current passing through it. B is wrong because the right-hand thumb rule finds the direction of the magnetic field lines around a straight current-carrying wire. C is wrong because Fleming's right-hand rule gives the direction of the induced current in a generator. Exam tip: left hand for motor, right hand for generator; forefinger = field, middle finger = current, thumb = motion.

The correct answer is A, vitamin B1. Beriberi is caused by a lack of thiamine, which is vitamin B1. Thiamine helps the body turn carbohydrates into energy and keeps nerves and the heart working, so its shortage weakens muscles and nerves (dry beriberi) or causes swelling and heart failure (wet beriberi). The disease was common in Asia among people living mainly on polished white rice, because milling strips away the thiamine-rich outer layer of the grain; whole grains, pulses, nuts and eggs supply it. Vitamin B1 is water-soluble, so the body stores little of it and needs a regular intake. B is wrong because vitamin A deficiency causes night blindness and xerophthalmia. C is wrong because vitamin C deficiency causes scurvy, with bleeding gums. D is wrong because vitamin D deficiency causes rickets in children and osteomalacia in adults. Exam tip: B1 beriberi, B3 pellagra, B12 pernicious anaemia, C scurvy, D rickets.

The correct answer is D, 9. Period 2 holds the eight elements from lithium (3) to neon (10), and group 17 is the halogen column, whose members have seven electrons in the outer shell. The element that is both in period 2 and in group 17 is fluorine, with electronic configuration 2, 7, and atomic number 9. You can work it out without memorising: period 2 means two shells, group 17 means seven valence electrons, so the electrons are 2 + 7 = 9, and in a neutral atom the number of electrons equals the atomic number. Fluorine is the most electronegative element and the most reactive non-metal. A, 8, is oxygen, which is in period 2 but in group 16 with six valence electrons. B, 7, is nitrogen, period 2, group 15. C, 10, is neon, period 2, group 18, a noble gas with a full shell. Exam tip: for periods 2 and 3, atomic number = electrons in the inner shells plus the group's last digit; 2 + 7 gives fluorine, 10 + 7 gives chlorine (17).

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 A, it is dipolar in nature. Water is called the universal solvent because its molecule is polar: the oxygen end carries a partial negative charge and the two hydrogen ends carry partial positive charges. The molecule is bent at an angle of about 104.5°, so these charges do not cancel out. When a salt such as sodium chloride is put in water, the negative oxygen ends surround the sodium ions and the positive hydrogen ends surround the chloride ions, pulling the crystal apart; this is called hydration. Water also forms hydrogen bonds with polar substances such as sugar and alcohol, which is why they dissolve easily, while non-polar oil does not. Option B is wrong because water is in fact a poor conductor of heat, and heat conduction has nothing to do with dissolving. Option C is wrong because high specific heat explains why water warms up slowly, not why it dissolves things. Option D is wrong because being an oxide of hydrogen does not by itself make a liquid a good solvent. Exam tip: polar water dissolves polar and ionic substances, because like dissolves like.

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 D, (i) - (c), (ii) - (b), (iii) - (a). Red cabbage is a natural acid-base indicator, methyl orange is a synthetic acid-base indicator, and onion and clove are olfactory indicators. An indicator tells whether a solution is acidic or basic. Natural indicators come from plants: litmus from lichen, turmeric, red cabbage leaves and coloured petals such as hydrangea and petunia. Synthetic indicators made in the laboratory include methyl orange, which is red in acid and yellow in base, and phenolphthalein, which is colourless in acid and pink in base. Olfactory indicators change their smell instead of their colour; onion, vanilla and clove lose their smell in a basic solution. A is wrong because it calls methyl orange an olfactory indicator. B is wrong because it labels red cabbage as olfactory. C is wrong because it puts onion and clove under natural colour indicators. Exam tip: change of smell = olfactory (onion, clove, vanilla); change of colour = litmus, turmeric, red cabbage; lab-made = methyl orange, phenolphthalein.

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, Al₂O₃ and ZnO. Aluminium oxide and zinc oxide behave like a base with acids and like an acid with bases, so both are amphoteric. With hydrochloric acid, aluminium oxide gives aluminium chloride and water. With sodium hydroxide, zinc oxide gives sodium zincate and water. The word amphoteric comes from the Greek for 'both', which is the easiest way to remember it. Most metal oxides are basic, while oxides of non-metals such as carbon dioxide and sulphur dioxide are acidic. Other common amphoteric oxides are those of lead and tin. Option A is wrong because copper(II) oxide is a basic oxide; it reacts with acids but not with bases. Option C is wrong for the same reason, as it also pairs aluminium oxide with basic copper oxide. Option D is wrong because only one pair, B, has both oxides amphoteric. Exam tip: remember the amphoteric four as Al, Zn, Pb and Sn, that is aluminium, zinc, lead and tin.

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, 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 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 D, Nucleus. The nucleus is called the master or control centre of the cell because it directs all the activities of the cell. It holds the chromosomes, which carry DNA, the genetic instructions for making proteins and for passing traits from parents to children. It is wrapped in a double membrane called the nuclear envelope, whose pores let messages move in and out. Robert Brown discovered the nucleus in 1831. Mature red blood cells of mammals have no nucleus. A is wrong because mitochondria release energy as ATP and are called the powerhouse of the cell. B is wrong because the endoplasmic reticulum is a network of membranes that makes and carries proteins and fats. C is wrong because the nucleolus is a small body inside the nucleus that makes ribosomes, so it is only a part of the control centre. Exam tip: Nucleus = control centre, Mitochondria = powerhouse, Ribosome = protein factory, Lysosome = suicide bag, Golgi body = packaging unit.

The correct answer is A, Platelets. Platelets are the tiny cell fragments that rush to a cut and start the clot. They are also called thrombocytes and are made in the bone marrow from large cells called megakaryocytes. A healthy adult has about 1.5 to 4 lakh platelets per cubic millimetre of blood, and each one lives for only 8 to 10 days. At a wound they stick together to form a plug and release chemicals that turn the soluble protein fibrinogen into fibrin threads, which trap blood cells and seal the leak. B is wrong because plasma proteins such as fibrinogen take part in clotting, but the paper marks platelets as the component that starts and aids clot formation. C is wrong because white blood cells fight infection, not bleeding. D is wrong because red blood cells carry oxygen with haemoglobin. Exam tip: RBC = oxygen, WBC = immunity, platelets = clotting; a falling platelet count is what dengue is known for.

The correct answer is B, Thyroid, Adrenal glands, Pituitary. The pituitary gland sends out hormones that order the thyroid and the adrenal glands to release their own hormones. The pituitary is a pea-sized gland attached to the base of the brain, and it is called the master gland because it controls several other endocrine glands. For example, it releases a thyroid-stimulating hormone that makes the thyroid produce thyroxine, and another hormone that makes the adrenal glands release theirs. NCERT's Class 8 science book notes that glands such as the thyroid and the adrenals secrete hormones on receiving a message from the pituitary. A is wrong because the pancreas releases insulin in response to blood sugar, and the thyroid does not command the other two. C is wrong because the testes and ovaries take their orders from the pituitary, not from the thyroid. D is wrong because the pituitary gives orders; it does not wait for orders from the thyroid. Exam tip: pituitary, master gland; thyroid, thyroxine; adrenal, adrenaline; pancreas, insulin.

The correct answer is B, Vitamin C. Vitamins fall into two groups: the water-soluble ones, which are vitamin C and the whole B-complex, and the fat-soluble ones, A, D, E and K. Vitamin C is ascorbic acid, found in citrus fruits, amla, guava and tomatoes; its deficiency causes scurvy, with bleeding gums and slow healing of wounds. Because water-soluble vitamins are not stored in the body and the extra is passed out in urine, they must be taken daily, while fat-soluble vitamins are stored in the liver and fatty tissue. A, Vitamin K, is fat-soluble and needed for blood clotting. C, Vitamin A, retinol, is fat-soluble and its deficiency causes night blindness. D, Vitamin D, calciferol, is fat-soluble, made in the skin in sunlight, and its lack causes rickets. Exam tip: remember "ADEK are fat-soluble"; everything else, B-complex and C, dissolves in water.