General Science Mixed Quiz: Set 1

The correct answer is B, newton. One newton is the force that gives a mass of one kilogram an acceleration of one metre per second squared, which follows directly from the equation force equals mass times acceleration. Its dimensional formula is therefore M L T⁻².

Option A, the joule, is the unit of work and energy: one joule is the work done when a force of one newton moves its point of application through one metre. Option C, the watt, is the unit of power, that is the rate of doing work, and equals one joule per second. Option D, the pascal, is the unit of pressure and equals one newton per square metre. All four are derived units named after scientists, and papers often list them together to see whether you can match each with its quantity.

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, 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 C, refraction of starlight. Starlight has to cross many layers of air before it reaches the eye, and these layers keep changing in temperature and density, so their refractive index keeps changing too. The light is bent a little differently every moment, the apparent position of the star shifts slightly and the amount of light entering the eye rises and falls. This flickering is what we call twinkling. A star is so far away that it acts as a point source, so the small shifts are easily seen. Planets are nearer and appear as tiny discs; light from the many points of the disc averages out, so planets do not twinkle. A, Diffraction, is the bending of light around edges and is not the cause. B, Reflection, sends light back from a surface and cannot make a star flicker. D, Scattering, of sunlight by air makes the sky blue but does not cause twinkling. Exam tip: twinkling and the early sunrise both come from atmospheric refraction; the blue sky and the red sunset come from scattering.

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, Gustav Robert Kirchhoff. This is Kirchhoff's first law, the current law or junction rule, which he stated in 1845. It says the total current entering a junction equals the total current leaving it, because charge cannot pile up or vanish at a point. So it is really the law of conservation of charge applied to a circuit node. Kirchhoff's second law, the voltage law or loop rule, says the algebraic sum of potential differences around any closed loop is zero, which follows from conservation of energy. Together the two laws let us solve circuits that Ohm's law alone cannot handle. A is wrong because Faraday's laws deal with electromagnetic induction and electrolysis, not junctions. B is wrong because Ohm's law relates voltage, current and resistance in a single conductor (V = IR). C is wrong because Victor Hess discovered cosmic rays and won the 1936 Nobel Prize in Physics. Exam tip: Kirchhoff current law = charge conserved at a junction; Kirchhoff voltage law = energy conserved around a loop.

The correct answer is C, Zn. Zinc has atomic number 30, meaning every zinc atom has 30 protons in its nucleus. It is the last element of the first transition series in period 4 of the modern periodic table, with the electronic configuration [Ar] 3d10 4s2, and it is placed in group 12. Zinc is a bluish-white metal used to galvanise iron against rust, to make brass with copper, and in dry cells. All four options are neighbours in the same period, which is why paper setters like this question: iron is 26, cobalt 27, nickel 28, copper 29 and zinc 30. A is wrong because Ni, nickel, has atomic number 28. B is wrong because Fe, iron, has atomic number 26. D is wrong because Co, cobalt, has atomic number 27. Exam tip: remember the run Fe 26, Co 27, Ni 28, Cu 29, Zn 30.

The correct answer is B, SF6. The name itself gives the formula: 'hexa' means six, so sulphur hexafluoride has one sulphur atom joined to six fluorine atoms, SF6. The molecule is octahedral in shape, with the six fluorine atoms arranged symmetrically around the sulphur. SF6 is a colourless, odourless, non-flammable and very unreactive gas, about five times heavier than air. Because it does not conduct electricity, it is used as an insulating gas inside high-voltage circuit breakers and switchgear. It is also one of the strongest greenhouse gases known, with a global warming potential thousands of times that of carbon dioxide, and it is listed under the Kyoto Protocol. A is wrong because S2F6 would need two sulphur atoms, which the name does not say. C is wrong because SF2 is sulphur difluoride, with only two fluorine atoms. D is wrong because S6F reverses the numbers and is not a real compound. Exam tip: mono 1, di 2, tri 3, tetra 4, penta 5, hexa 6; SF6 = one sulphur, six fluorine, used in electrical switchgear.

The correct answer is B, Baking soda. Its chemical name is sodium hydrogen carbonate and its formula is NaHCO3. It is a mild, non-corrosive base made by the Solvay process, in which brine is treated with ammonia and carbon dioxide. When heated it gives off carbon dioxide, which is why it makes cakes rise; it is also used in antacids, soda-acid fire extinguishers and as a cleaning agent. Note the trap in this question: baking soda and baking powder are different things. A is wrong because baking powder is a mixture of baking soda with a mild edible acid such as tartaric acid, not a single compound. C is wrong because washing soda is sodium carbonate decahydrate, Na2CO3.10H2O, used to soften hard water and in glass and soap making. D is wrong because plaster of Paris is calcium sulphate hemihydrate, CaSO4.1/2H2O, used for casts and moulds. Exam tip: baking soda NaHCO3, washing soda Na2CO3.10H2O, plaster of Paris CaSO4.1/2H2O, bleaching powder CaOCl2.

The correct answer is C, Zinc. Galvanisation is the coating of iron or steel with a thin layer of zinc so that the iron underneath does not rust. Zinc sits above iron in the reactivity series, so even when the coating is scratched, zinc corrodes first and keeps protecting the iron; this is called sacrificial protection. The zinc layer is usually put on by dipping the article in molten zinc (hot-dip galvanising) or by electroplating. Galvanised sheets are used for roofs, water pipes, buckets and electricity poles. A, Gallium, is a rare, low-melting metal and is never used for rust protection. B, Aluminum, forms its own protective oxide layer, but coating iron with aluminium is not called galvanisation. D, Silver, is too costly and is less reactive than iron, so it would not protect it sacrificially. Exam tip: galvanisation means a zinc coating on iron; a tin coating on iron is called tinning.

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 C, N2O. Laughing gas is nitrous oxide, N2O, a colourless gas with a faintly sweet smell that makes people giggle and feel light-headed when they breathe it in. It was first prepared by Joseph Priestley in 1772, and Humphry Davy studied its effects and gave it the popular name. Dentists and surgeons use it mixed with oxygen as a mild anaesthetic and pain-killer, and it is also the propellant in whipped-cream cans. In the laboratory it is made by gently heating ammonium nitrate. It is a greenhouse gas too, and it damages the ozone layer. A is wrong because NO is nitric oxide, a colourless gas that turns brown in air. B is wrong because N2O3 is dinitrogen trioxide, a blue liquid at low temperature. D is wrong because NO2 is nitrogen dioxide, the reddish-brown, poisonous gas seen in vehicle smoke and acid rain. Exam tip: laughing gas = nitrous oxide = N2O, discovered by Priestley, used as a dental anaesthetic.

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 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, 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 A, Melatonin. The pineal gland, a small pine-cone-shaped gland deep in the brain, secretes melatonin. Melatonin controls the body's day-night rhythm, called the circadian rhythm, and helps regulate sleep. The gland releases more melatonin in darkness and less in bright light, which is why bright screens late at night can disturb sleep. Melatonin also plays a part in the timing of puberty and in seasonal changes in some animals. The French philosopher Descartes once called the pineal gland 'the seat of the soul'. B is wrong because progesterone is made mainly by the ovaries (the corpus luteum) and helps prepare for and maintain pregnancy. C is wrong because epinephrine, or adrenaline, is released by the adrenal medulla and prepares the body for 'fight or flight'. D is wrong because insulin is made by the beta cells of the islets of Langerhans in the pancreas and lowers blood sugar. Exam tip: pineal gland, melatonin, sleep; pancreas, insulin; adrenal medulla, adrenaline.

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 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 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, 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.