General Science Mixed Quiz: Set 8

The correct answer is B, amount of substance. The mole is the chemist's counting unit: one mole of any substance contains the Avogadro number of particles, about six followed by twenty-three zeros, whether those particles are atoms, molecules or ions. It is one of the seven base units of the SI system and is written with the symbol mol.

Option A, mass, has the kilogram as its base unit; the two are related through molar mass but are not the same quantity. Option C, density, is a derived quantity measured in kilograms per cubic metre. Option D, volume, is also derived and is measured in cubic metres, with the litre used as a convenient practical unit. Questions of this type test the pairing of each base unit with its own quantity, so learn all seven pairs together.

The correct answer is B, A bottle opener. Levers are grouped by where the fulcrum, the load and the effort sit. In a second class lever the load lies between the fulcrum and the effort. In a bottle opener the rim of the cap is the fulcrum at the tip, the cap being lifted is the load in the middle, and your hand applies the effort at the far end. Such levers always multiply force because the effort arm is longer; a wheelbarrow and a nutcracker work the same way. A, A pair of scissors, is a first class lever, with the pivot between the effort and the load. C, A cricket bat, is a third class lever: the lower hand applies the effort between the top hand, which acts as the fulcrum, and the ball. D, A bow and arrow, works by storing energy in the bent bow like a spring, not by placing the load between the fulcrum and the effort. Exam tip: first class has the fulcrum in the middle, second class the load in the middle, third class the effort in the middle.

The correct answer is C, a concave lens of suitable power. A concave lens spreads the light rays slightly before they enter the eye, so the image moves back onto the retina. In myopia, or short-sightedness, a person sees nearby objects clearly but distant objects look blurred. It happens when the eyeball is too long or the eye lens is too curved, so light from far objects meets in front of the retina. Concave lenses have negative power, so spectacles for myopia carry a minus number such as -2.0 D (dioptre). A is wrong because a biconvex lens brings rays together and would make the blur worse. B is wrong because a plain glass plate has no power and does not change where the rays meet. D is wrong because a convex lens corrects hypermetropia, or long-sightedness, in which the image forms behind the retina. Exam tip: Myopia = concave (minus) lens; Hypermetropia = convex (plus) lens; Presbyopia in old age = bifocal lens; Astigmatism = cylindrical lens.

The correct answer is D, General theory of relativity. LIGO, the Laser Interferometer Gravitational-Wave Observatory in the USA, detected gravitational waves for the first time in September 2015 (announced in February 2016), and such waves were predicted by Einstein's general theory of relativity in 1916. General relativity treats gravity as the curving of space-time and says that huge accelerating masses, like two black holes spiralling into each other, send ripples through space-time at the speed of light. LIGO's two detectors at Hanford and Livingston measured a change in arm length smaller than the width of a proton. India is building a third detector, LIGO-India, at Hingoli in Maharashtra. A, String theory, has made no prediction that any experiment has yet confirmed. B, Special relativity, deals with motion at constant speed and does not include gravity. C, Quantum mechanics, describes atoms and particles, not gravitational waves. Exam tip: LIGO means gravitational waves, which means general relativity; the 2017 Physics Nobel went to Weiss, Barish and Thorne for it.

The correct answer is D, f-block. The inner transition elements are the lanthanides and actinides, in which electrons fill the f-orbitals, so they form the f-block of the periodic table. They are placed in two separate rows at the bottom of the table so that the table does not become too wide. The lanthanides run from cerium to lutetium and are also called rare earth elements; the actinides run from thorium to lawrencium and are all radioactive. Uranium and plutonium, used in nuclear power, are actinides. Option A is wrong because the d-block holds the transition elements such as iron, copper and zinc, in groups 3 to 12. Option B is wrong because the p-block holds groups 13 to 18, including the halogens and the noble gases. Option C is wrong because the s-block holds groups 1 and 2, the alkali and alkaline earth metals. Exam tip: the d-block has the transition elements; the f-block has the inner transition elements, the lanthanides and actinides.

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, Aluminium. Aluminium naturally forms a thin layer of aluminium oxide when it is exposed to air, and this layer protects it from further corrosion. In anodising, the layer is made thicker on purpose. A clean aluminium article is made the anode, the positive electrode, in an electrolytic bath of dilute sulphuric acid, and the oxygen gas released at the anode reacts with the metal to build a thick oxide coat. This coat resists corrosion and scratches and can easily be dyed in attractive colours, which is why anodised aluminium is used for pressure cookers, window frames and many household articles. Option A is wrong because silver does not form a protective oxide coat; it turns black by forming silver sulphide. Option C is wrong because gold hardly reacts with air at all, so it needs no such coating. Option D is wrong because copper, in moist air, gets a green coat of basic copper carbonate, not an anodised oxide layer. Exam tip: anodising means a thick oxide layer on aluminium; galvanising means a coat of zinc on iron.

The correct answer is B, 1831. In 1831 the British scientist Michael Faraday showed that a changing magnetic field produces an electric current in a nearby coil. He moved a magnet in and out of a coil of wire and saw a galvanometer needle move, and he also found that switching a current on and off in one coil induced a current in a second coil wound on the same iron ring. This is electromagnetic induction, the working principle of the electric generator (dynamo) and the transformer. The SI unit of capacitance, the farad, is named after him. A is wrong because 1853 is more than twenty years after the discovery. C is wrong because 1820 is the year Hans Christian Oersted found that an electric current produces a magnetic field, the reverse effect. D is wrong because 1875 has no link with this discovery. Exam tip: Oersted 1820, current makes magnetism; Faraday 1831, changing magnetism makes current.

The correct answer is D, Proteins. Kwashiorkor is caused by a severe lack of protein in the diet, even when the child gets some calories from starchy food. It usually strikes children aged one to five after they stop breastfeeding and are fed mostly rice, maize or cassava. The tell-tale signs are a swollen belly and puffy legs due to fluid retention (oedema), a moon face, peeling skin, thin reddish hair and poor growth. The word comes from Ghana and is often explained as the sickness of the older child pushed off the breast when a new baby arrives. Its cousin marasmus comes from a lack of both protein and calories and leaves the child wasted, with no swelling. A is wrong, because mineral shortages cause other diseases, such as anaemia from lack of iron and goitre from lack of iodine. B is wrong, because vitamin deficiencies cause scurvy, rickets and night blindness, not kwashiorkor. C is wrong, because a lack of fat is not what causes kwashiorkor. Exam tip: kwashiorkor, protein only, swollen belly; marasmus, protein and calories, wasting.

The correct answer is B, milk of magnesia. Milk of magnesia is a milky white suspension of magnesium hydroxide, Mg(OH)2, in water. It is a mild base, so it neutralises the extra hydrochloric acid in the stomach that causes acidity and heartburn; the reaction gives magnesium chloride and water. In larger doses it draws water into the intestine and works as a laxative. This antacid is a textbook example of neutralisation, where an acid and a base react to form a salt and water. A is wrong because fused magnesia is magnesium oxide melted in an electric arc furnace and used as a heat-resistant material in furnace linings. C is wrong because magnesia alba is a basic magnesium carbonate, a white powder. D is wrong because caustic-calcined magnesia is magnesium oxide made by heating at lower temperatures and used in industry and farming. Exam tip: milk of magnesia is Mg(OH)2, an antacid base that neutralises stomach HCl.

The correct answer is B, Geitonogamy. Geitonogamy is the transfer of pollen grains from the anther of one flower to the stigma of another flower on the same plant. In the way it happens it is like cross-pollination, because an outside agent such as an insect or the wind carries the pollen; but genetically it is like self-pollination, because the pollen comes from the same plant and brings no new genes. The word comes from the Greek geiton, meaning neighbour, which is an easy way to remember it: pollen goes to the neighbouring flower. Option A is wrong because autogamy is pollination within the same flower, where pollen reaches the stigma of the very flower that produced it, as in closed cleistogamous flowers. Option C is wrong because xenogamy is the transfer of pollen to a flower of a different plant, the only type that brings genetically different pollen to the stigma. Option D is wrong because geitonogamy is the exact name for this process. Exam tip: autogamy same flower, geitonogamy same plant, xenogamy different plant.

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, 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, 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 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 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 B, 746 watts. The horsepower is an older practical unit of power that survives in the rating of engines, pumps and motors, and it equals about 746 watts. The watt itself is the SI unit of power and means one joule of work done in one second.

Option A, 500 watts, and Option D, 1,200 watts, correspond to no standard unit. Option C, 1,000 watts, is one kilowatt, which is a different and very common unit: the electricity used at home is billed in kilowatt hours, popularly called units, where one kilowatt hour is the energy used by a one kilowatt appliance running for one hour. Keep the two apart, since a question often offers the kilowatt as a distractor for horsepower.

The correct answer is C, Both I and II. Atomicity is the number of atoms in one molecule of an element, and it is why we write nitrogen gas as N2 and not just N. Nitrogen gas exists as N2, two atoms joined by a strong triple bond, so it is diatomic, like oxygen, hydrogen and chlorine. Sulphur exists as S8, a crown-shaped ring of eight atoms, so it is polyatomic. Phosphorus, as P4, is tetra-atomic, ozone (O3) is triatomic, and noble gases such as helium and argon are monoatomic because they exist as single atoms. These examples are listed in the NCERT Class 9 chapter on atoms and molecules. Option A is wrong because it accepts only the first pair, though the sulphur pair is also right. Option B is wrong because both pairs are correct, so 'neither' cannot be the answer. Option D is wrong because it accepts only the sulphur pair and leaves out nitrogen, which is correctly diatomic. Exam tip: He mono, N2 di, O3 tri, P4 tetra, S8 poly.

The correct answer is C, Vitamin B1. Thiamin (thiamine) is vitamin B1, a water-soluble vitamin that helps the body turn carbohydrates into energy and keeps the nerves and heart working well. Its deficiency causes beriberi, a disease that weakens the muscles and nerves. It was once common among people who ate mostly polished rice, because polishing removes the thiamin-rich outer layer of the grain. Good sources are whole grains, pulses, nuts and yeast. Being water-soluble, it is not stored in the body for long and must come from the daily diet. A is wrong because vitamin B2 is riboflavin, whose deficiency causes cracks at the corners of the mouth. B is wrong because vitamin B3 is niacin, whose deficiency causes pellagra. D is wrong because vitamin B12 is cobalamin, which contains cobalt, and its deficiency causes pernicious anaemia. Exam tip: B1 thiamin and beriberi; B2 riboflavin; B3 niacin and pellagra; B12 cobalamin and pernicious anaemia.

The correct answer is C, Anabaena. Anabaena is a cyanobacterium, a prokaryote with no true nucleus, and all prokaryotes are placed in Monera. In R.H. Whittaker's five-kingdom classification (1969), Monera holds the bacteria and the cyanobacteria, or blue-green algae, whose cells have no nuclear membrane and no membrane-bound organelles. Anabaena grows as chains of cells and has special thick-walled cells called heterocysts that fix nitrogen from the air. It lives inside the small water fern Azolla, which is why Azolla is used as a biofertiliser in paddy fields. Option A is wrong because diatoms are single-celled eukaryotes with glass-like silica walls, placed in Protista; their deposits form diatomaceous earth. Option B is wrong because Euglena is a protist that makes its own food in light but feeds like an animal in the dark. Option D is wrong because Ulothrix is a filamentous green alga with a true nucleus, grouped with plants. Exam tip: no true nucleus means Monera; Anabaena and Nostoc are the nitrogen-fixing cyanobacteria to remember.