General Science Mixed Quiz: Set 67

The correct answer is B, hexamethylenediamine and adipic acid. Nylon-6,6 is a polyamide formed when hexamethylenediamine condenses with adipic acid, with a molecule of water eliminated at each linkage; the name records that each monomer contributes a chain of six carbon atoms. It is used for ropes, tyre cord, brush bristles and parachute fabric. A is wrong because caprolactam alone gives nylon-6, a related but different polyamide. C is wrong because ethylene glycol with terephthalic acid gives the polyester terylene, also called dacron, and in bottle form polyethylene terephthalate. D is wrong because phenol with formaldehyde gives bakelite, a thermosetting plastic and not a fibre at all. The naming rule is worth carrying into the hall: a nylon with two numbers is made from two monomers, one supplying the diamine and the other the diacid, while a nylon with one number comes from a single monomer, so nylon-6,6 must be the pair and nylon-6 the single one.

The correct answer is B, Concrete. Concrete is the building material made by mixing cement with coarse aggregate such as gravel, fine aggregate such as sand, and water.

The cement and water react in a process called hydration, which sets into a hard mass and binds the aggregate together. A common ratio for ordinary work is one part cement, two parts sand and four parts gravel, written as 1:2:4. Concrete is strong in compression but weak in tension, so steel bars are embedded in it to make reinforced cement concrete, the material of most modern buildings, bridges and dams.

Option A, mortar, is cement or lime with sand and water only, with no coarse aggregate, and is used to join bricks. Option C, slurry, is any thin, pourable mix of a solid in a liquid. Option D, a moderator, is the material that slows neutrons in a nuclear reactor.

Exam tip: mortar has no gravel; concrete has gravel; adding steel gives RCC.

The correct answer is B, 96,500 coulombs. One faraday is the charge carried by one mole of electrons, obtained by multiplying the charge on a single electron by the Avogadro number, and it comes to about 96,500 coulombs; passing one faraday through an electrolyte liberates one gram equivalent of the substance at an electrode. A is wrong because 9,650 coulombs is one-tenth of the correct value and is a careless-reading trap. C is wrong because the figure 1.6 belongs to the charge on one electron, which is 1.6 into ten raised to the power minus nineteen coulombs, not to the faraday. D is wrong because 6.023 into ten raised to the power twenty-three is the Avogadro number, a count of particles and not a quantity of charge, though the two are linked in the very calculation that gives the faraday.

The correct answer is D, Zygote. The fusion of a male gamete with a female gamete is called fertilisation, and the single cell it produces is the zygote. The male gamete in animals is the sperm and the female gamete is the egg or ovum. Each gamete carries half the normal number of chromosomes, so the zygote gets a full set again: in human beings 23 chromosomes come from the sperm and 23 from the egg, making 46. The zygote then divides again and again, travels down the fallopian tube and settles in the wall of the uterus. Option A is wrong because the ovum is the female gamete itself, one of the two cells that fuse, not the result. Option C is wrong because the embryo is the ball of cells formed after the zygote starts dividing. Option B is wrong because the foetus is a still later stage, when the organs have taken shape. Exam tip: remember the order gametes to zygote to embryo to foetus.

The correct answer is B, sulphur. Vulcanisation is the heating of raw rubber with sulphur, which forms short cross-links between the long isoprene chains. Raw rubber is soft, sticky when warm and brittle when cold; the vulcanised product is strong, far more elastic and stable over a wide range of temperature. Tyre rubber carries a few per cent of sulphur and very hard ebonite much more. A, carbon, is a careful distractor: carbon black is indeed added to tyre rubber as a filler to resist wear, but adding it is not vulcanisation and it forms no cross-links. C, phosphorus, is wrong because it has no role in rubber processing. D, silicon, is wrong; silicone rubbers are a separate class of synthetic polymer and are not made by vulcanising natural rubber. Note too that vulcanisation was discovered by Charles Goodyear, which is a fact examiners sometimes ask alongside the role of sulphur.

The correct answer is C, Hepatitis B. The hepatitis B vaccine was the first vaccine made by recombinant DNA technology. Scientists cut out the gene for the surface protein of the hepatitis B virus and put it into yeast cells; the yeast then made that protein in large amounts, and the purified protein is injected as the vaccine. Because only one viral protein is used and no whole virus is involved, the vaccine cannot cause the disease, which is what makes recombinant vaccines safe. It was licensed in the mid 1980s and in India it is part of the pentavalent shot given to infants. A is wrong because the polio vaccine is either the killed virus of Salk or the weakened live virus of Sabin. B is wrong because no vaccine against AIDS has been licensed so far. D is wrong because the smallpox vaccine used the live vaccinia virus, and the disease was declared eradicated in 1980. Exam tip: hepatitis B, first recombinant vaccine, made in yeast from the surface antigen gene.

The correct answer is B, the cathode. The metal ions in the plating bath carry a positive charge, so they move towards the negative electrode and are reduced to metal there; the article must therefore be the cathode for the coating to build up on it. A is wrong because the anode is a plate of the pure plating metal, which dissolves into the solution as the plating proceeds and so keeps the concentration of the bath steady, which is why the bath does not have to be renewed often. C is wrong because the electrolyte is a solution of a salt of the plating metal, such as a copper salt for copper plating, and is not an electrode at all. D is wrong because the polarity cannot be chosen freely: reversing it would strip metal from the article instead of depositing it, which is in fact how electro-polishing and anodising work.

The correct answer is A, Ashwagandha. Ashwagandha, whose botanical name is Withania somnifera, is called winter cherry in English because of the small red berry it bears inside a papery cover; it is also called Indian ginseng. The part used is the root, which in Ayurveda is given as a tonic for weakness, stress and sleeplessness, and the plant's Sanskrit name comes from the horse-like smell of the fresh root. It is a hardy shrub of dry regions, so Rajasthan, Madhya Pradesh and Gujarat are the main growing states; the Nagauri type from Nagaur in Rajasthan and the crop around Mandsaur and Neemuch in Madhya Pradesh are the best known. B is wrong because rose is an ornamental and perfume crop, not a winter cherry. C is wrong because lily is a garden flower grown from bulbs. D is wrong because chandni is an ornamental flowering shrub grown for its white flowers. Exam tip: Ashwagandha, Withania somnifera, winter cherry or Indian ginseng, root used.

The correct answer is C, polyvinyl chloride. Polyvinyl chloride has linear chains held to one another only by weak forces, so it softens when heated and hardens when cooled and can be melted and moulded again and again; that reversibility is what makes a plastic thermoplastic, and it is also what allows such plastics to be recycled by melting. A, bakelite, is wrong because its chains are tied together by covalent cross-links into one network, so it is thermosetting and only chars on strong heating. B, melamine-formaldehyde, is wrong for the same reason, and that is exactly why melamine crockery keeps its shape in hot water. D, urea-formaldehyde, is wrong because it too is a cross-linked thermosetting resin, used in adhesives and laminates. The quick test in the examination hall is to ask whether the plastic can be melted again: if it can, it is a thermoplastic.

The correct answer is B, Galileo Galilei. Galileo was the first to argue that, with air resistance removed, every body falls with the same acceleration regardless of its mass. He reached this by rolling balls down inclined planes and timing them, and the idea is linked in popular accounts with his experiment from the Leaning Tower of Pisa. This overturned the older belief of Aristotle that heavier bodies fall faster. The acceleration he described is g, about 9.8 metres per second squared near the earth. A is wrong because Einstein built on this in the general theory of relativity through the equivalence principle, long afterwards. C is wrong because Edison was an inventor of the electric lamp and phonograph and did no work on falling bodies. D is wrong because Newton, born the year Galileo died, later explained why this happens through his law of gravitation. Exam tip: remember the order - Galileo found that all bodies fall alike, Newton explained the cause.

The correct answer is C, chlorine. In the chlor-alkali process a concentrated solution of sodium chloride is electrolysed; chloride ions are oxidised at the anode and come off as chlorine gas, hydrogen is set free at the cathode, and sodium hydroxide remains in the solution, which is why the industry yields three useful products at once. A is wrong because hydrogen appears at the cathode, not the anode. B is wrong because oxygen is the anode product when water or a dilute solution of an acid or of a salt of a very reactive metal is electrolysed; in concentrated brine the chloride ion is discharged in preference to water. D is wrong because the solution contains no carbonate or carbon source at all, so carbon dioxide cannot be formed. Remember the trio: chlorine, hydrogen and caustic soda from brine.

The correct answer is C, Thallophyta. Litmus is a purple dye taken from lichens, and in the classification used in school science lichens are placed in Thallophyta, the group of simple plants whose body is an undifferentiated thallus with no true root, stem or leaf. Algae and fungi belong to the same group, and a lichen is in fact a partnership of an alga and a fungus living together. Litmus is a natural indicator: it stays purple in a neutral solution, turns red in acid and blue in base, and is used both as a solution and as litmus paper. Option A is wrong because gymnosperms are well developed plants with naked seeds, such as pine and cycas. Option B is wrong because pteridophytes, the ferns, are the first plants with vascular tissue. Option D is wrong because bryophytes such as moss and Marchantia are called the amphibians of the plant kingdom. Exam tip: litmus is red in acid, blue in base and purple when neutral.

The correct answer is B, a semi-synthetic fibre made from cellulose. Rayon is made by dissolving the cellulose of wood pulp, forcing the solution through fine holes and regenerating the cellulose as a thread. The raw material is natural and the processing is chemical, so rayon is semi-synthetic, and because it takes dye well and feels like silk it is called artificial silk. A is wrong because the natural protein fibres are wool, which is keratin, and silk, which is fibroin. C is wrong because the synthetic polyamide fibre is nylon, built entirely from petrochemical monomers. D is wrong because rayon is a fibre, not a plastic, and nothing about it is cross-linked or thermosetting; cellulose acetate and vulcanised rubber are the other standard examples of semi-synthetic polymers. Remember the three-way split of source as natural, semi-synthetic and synthetic, and rayon will always fall in the middle.

The correct answer is B, Nitrogen. An ordinary incandescent bulb is filled with an unreactive gas, nitrogen usually mixed with argon, so that the white-hot tungsten filament does not burn away. The filament works at about 2500 degrees Celsius, and in air the tungsten would oxidise within seconds. Nitrogen and argon do not react with tungsten, and the gas pressure inside also slows the evaporation of the metal, so the filament lasts longer and the glass does not blacken quickly. A is wrong because halogens such as iodine and bromine are added only in halogen lamps, a special high-temperature type, not in the common bulb. C is wrong because carbon dioxide would release oxygen at that temperature and attack the filament. D is wrong because hydrogen is highly inflammable and would make the bulb dangerous. Exam tip: filament is tungsten, melting point about 3400 degrees Celsius, and the bulb is filled with nitrogen and argon.

The correct answer is B, the lead-acid cell. Its reaction is reversible, so passing a current through it in the opposite direction converts the products back into lead and lead dioxide and the cell can be used again; such a cell is called a secondary or storage cell, and the car battery is the common example. A is wrong because the dry cell of the Leclanche type is a primary cell: once the zinc container and the manganese dioxide are consumed the cell is thrown away, and attempting to recharge it can make it leak. C is wrong because the Daniell cell, with its zinc and copper electrodes in their own salt solutions, is a classic primary cell of the laboratory. D is wrong because a mercury button cell of the kind used in watches is also a primary cell. Nickel-cadmium and lithium-ion cells are the other important secondary cells.

The correct answer is C. Ultraviolet light is a transverse wave, not a longitudinal one, so this statement is the wrong one. In an electromagnetic wave the electric and magnetic fields vibrate at right angles to each other and to the direction the wave travels, which is the definition of a transverse wave. Longitudinal waves need a material to squeeze and stretch, and sound is the standard example. Option A is correct because ultraviolet light sits in the electromagnetic spectrum between visible light and X-rays. Option B is correct because electromagnetic waves need no medium and cross empty space, which is how the Sun's ultraviolet rays reach the earth. Option D is correct because ultraviolet wavelengths run from about 400 nanometres down to 10 nanometres, shorter than violet light, and this higher energy is what burns skin and is absorbed by the ozone layer. Exam tip: all electromagnetic waves are transverse; only mechanical waves such as sound can be longitudinal.

The correct answer is A, butadiene and styrene. Buna-S, also called styrene-butadiene rubber, is made by copolymerising 1,3-butadiene with styrene; the S in the name stands for styrene. It wears better than natural rubber and is the commonest rubber in tyres and shoe soles. B, butadiene and acrylonitrile, is the main trap: that combination gives Buna-N, whose resistance to petrol and oil makes it the choice for fuel hoses and oil seals, and the N stands for the nitrile group. C is wrong because isoprene is the monomer of natural rubber and chloroprene of neoprene, and the two are not copolymerised together in this way. D is wrong because ethene and propene give polyolefin plastics and elastomers, not Buna-S. So read the letter at the end of the name: S for styrene and N for nitrile, and the question answers itself.

The correct answer is C, zinc. In the Leclanche dry cell the outer container itself is made of zinc and acts as the anode, being oxidised to zinc ions as the cell works, which is why an old cell often leaks when the container is eaten through. A is wrong because copper has no part in this cell; it is the cathode metal of the Daniell cell, a different arrangement. B is wrong because the graphite rod in the centre of the dry cell is the cathode, an inert conductor that carries the current away from the reduction reaction rather than taking part in it. D is wrong because manganese dioxide is the depolariser packed around the graphite rod: it is reduced and absorbs the hydrogen that would otherwise collect and stop the cell, but it is not the anode. The electrolyte is a moist paste of ammonium chloride and zinc chloride, and the cell gives about 1.5 volts.

The correct answer is A, expanded polystyrene. Thermocol is polystyrene expanded with a blowing agent so that the solid becomes a rigid foam of tiny closed cells. The trapped air makes it very light and a poor conductor of heat, so it is used for packing fragile goods, for disposable food boxes and for insulating walls and cold rooms. B is wrong because the foam made from polythene is a softer, more flexible packing material and is not thermocol. C is wrong because bakelite is a hard cross-linked thermosetting resin that cannot be expanded into such a foam and is used for switches and handles. D is wrong because foamed polyvinyl chloride exists as a board for signs and cladding, but it is denser and is not the material called thermocol.

The correct answer is A, dilute sulphuric acid. The lead-acid cell has a spongy lead negative plate and a lead dioxide positive plate dipped in dilute sulphuric acid, and as the cell discharges both plates turn to lead sulphate while the acid becomes weaker, which is why its state of charge can be judged from the specific gravity of the acid. B is wrong because concentrated nitric acid is a strong oxidising agent that would attack the lead plates and the container instead of working as an electrolyte. C is wrong because the moist paste of ammonium chloride belongs to the Leclanche dry cell, a primary cell that cannot be recharged. D is wrong because potassium hydroxide is the alkaline electrolyte of the nickel-cadmium and nickel-iron cells, which is a different family of secondary cells. Each lead-acid cell gives about two volts, so six in series make a twelve volt battery.