General Science Mixed Quiz: Set 78

The correct answer is C, with y-intercept u. The equation v = u + at has the form y = c + mx, so the graph is a straight line that cuts the velocity axis at u and has slope a.

On a velocity-time graph, time is on the x-axis and velocity on the y-axis. At t = 0 the velocity is u, so the line starts from the point (0, u) on the y-axis; that value is the y-intercept. The slope of a velocity-time graph gives the acceleration, here a, and the area under the line gives the displacement. Only if the body starts from rest (u = 0) does the line pass through the origin.

A is wrong: the line passes through the origin only when u = 0, which is not given.

B is wrong: u is the value of velocity, read on the y-axis, not an x-intercept.

D is wrong: the slope of the line is the acceleration a, not the initial velocity u.

Exam tip: on a v-t graph, slope = acceleration, area under the graph = displacement, y-intercept = initial velocity.

The correct answer is C, Passing water through a cation exchange and an anion exchange resin bed. Together the two resins take out every dissolved ion, which leaves demineralised water.

In the cation exchange resin (written RH), metal ions such as Ca2+, Mg2+ and Na+ are swapped for H+ ions. The water then passes through the anion exchange resin (written R'OH), where chloride, sulphate and bicarbonate ions are swapped for OH− ions. The H+ and OH− so released join to form water, so no salt is left. This deionised water is used in laboratories, batteries and boilers.

A is wrong: a microfiltration membrane stops suspended particles and microbes, not dissolved salts.

B is wrong: Calgon (sodium hexametaphosphate) only ties up calcium and magnesium ions; the salts stay dissolved in the water.

D is wrong: boiling removes only temporary hardness caused by bicarbonates; chlorides and sulphates remain.

Exam tip: cation resin gives H+, anion resin gives OH−; both together = demineralised (deionised) water.

The correct answer is C, 1 and 2 only. By Coulomb's law the force F = kq₁q₂/r² comes out positive, meaning repulsive, whenever the two charges have the same sign.

In Coulomb's law the sign of the force follows the product of the two charges. Two positive charges give a positive product, and two negative charges also give a positive product, because a negative times a negative is positive. A positive value means the force is repulsive: like charges repel. When one charge is positive and the other negative, the product is negative and the force is attractive: unlike charges attract.

A is wrong: two positive charges do give a positive force, but so do two negative charges.

B is wrong: it misses the case of two positive charges.

D is wrong: opposite charges give a negative product, that is an attractive force, so statement 3 is wrong.

Exam tip: like charges repel (positive force), unlike charges attract (negative force); the force varies as 1/r².

The correct answer is C, 2 × 10⁵ A.U. One parsec equals about 2,06,265 astronomical units, which rounds to 2 × 10⁵ A.U.

An astronomical unit is the mean distance between the Earth and the Sun, about 1·5 × 10¹¹ m. A parsec is the distance at which one astronomical unit subtends an angle of one second of arc; the name comes from "parallax of one arcsecond". Since one radian holds about 2,06,265 arcseconds, a parsec is that many astronomical units, roughly 3·26 light years or 3·1 × 10¹⁶ m. Astronomers use it for distances between stars.

A is wrong: 2,000 A.U. is about a hundred times too small.

B is wrong: 20,000 A.U. is still ten times smaller than a parsec.

D is wrong: 2 × 10⁶ A.U. is ten times larger than a parsec.

Exam tip: 1 parsec ≈ 2·06 × 10⁵ A.U. ≈ 3·26 light years; order of size is A.U. < light year < parsec.

The correct answer is C, Smooth muscle. Smooth muscle is a muscular tissue, one of the four basic animal tissues, not a connective tissue.

Animal tissues are of four kinds: epithelial, connective, muscular and nervous. Connective tissues have cells spread in a matrix and bind or support other parts; they include bone, cartilage, blood, areolar tissue, adipose tissue, ligaments and tendons. Smooth muscle is made of spindle-shaped, unstriated cells that contract on their own, without our will, in the walls of the stomach, intestines, blood vessels and the iris.

A is wrong: a ligament is dense connective tissue joining bone to bone; it is strong and elastic.

B is wrong: a tendon is dense connective tissue joining muscle to bone; it is strong but has little elasticity.

D is wrong: cartilage is a connective tissue with a firm matrix, found in the nose, ear, trachea and joint surfaces.

Exam tip: ligament = bone to bone, tendon = muscle to bone; muscles (smooth, skeletal, cardiac) are a separate tissue.

The correct answer is C, Thiourea (accelerator). Accelerators speed up the vulcanisation of rubber; they are not a part of paint.

An oil paint is made of a pigment that gives colour and covering power, a vehicle or drying oil such as linseed oil that binds the film, a thinner that makes it easy to spread, a drier that speeds up hardening, fillers or extenders that add body, and an anti-skinning agent that stops a skin forming in the tin. Titanium dioxide is the most widely used white pigment, turpentine is the classic thinner, and polyhydroxy phenols are used as anti-skinning agents. Thiourea and similar compounds belong to rubber technology, where accelerators shorten the time sulphur takes to cross-link rubber.

A is wrong: turpentine oil is a standard thinner in paint.

B is wrong: polyhydroxy phenols are used in paint as anti-skinning agents.

D is wrong: titanium dioxide is the main white pigment in paints.

Exam tip: paint = pigment + vehicle (linseed oil) + thinner (turpentine) + drier + filler + anti-skinning agent.

The correct answer is D, Aerenchyma. Aerenchyma is a kind of parenchyma whose cells enclose large air-filled spaces.

These air cavities keep aquatic plants such as water hyacinth, lotus and Hydrilla afloat and let oxygen move down to roots and stems that sit in waterlogged soil or under water. Rice and many marsh plants also form aerenchyma in their roots when the soil is flooded. The name itself helps: 'aer' means air and 'enchyma' means tissue.

A is wrong: sclerenchyma has thick, lignified walls and dead cells packed close together; it gives hardness, as in coconut husk.

B is wrong: meristem cells are small, living, dividing cells packed without intercellular spaces.

C is wrong: collenchyma has living cells thickened at the corners with very little space between them; it gives flexibility to stems and leaf stalks.

Exam tip: aerenchyma = air spaces and buoyancy in water plants; sclerenchyma = hardness; collenchyma = flexibility.

The correct answer is A, Crown Gall. Crown gall is caused by the bacterium Agrobacterium tumefaciens, which enters through a wound near the base, or crown, of the stem and makes the plant grow rough tumour-like swellings there. The bacterium works by pushing a piece of its own Ti plasmid into the plant's cells and forcing them to divide, and that natural trick is why laboratories use it as a vector to carry new genes into plants. Grapevine, apple, rose, walnut and stone fruits suffer the most. Option B is wrong because mosaic diseases, such as tobacco mosaic, are caused by viruses that mottle the leaves in light and dark patches. Option C is wrong because smut of wheat, bajra and sugarcane is a fungal disease that fills the ear with black powdery spores. Option D is wrong because white blister, or white rust, of crucifers such as mustard is also fungal and raises white blisters on leaves and stems. Exam tip: bacterial — crown gall, citrus canker, bacterial blight of rice; viral — mosaic, leaf curl; fungal — smut, rust, blight.

The correct answer is A, flatworms, the phylum Platyhelminthes. Flame cells, also called solenocytes, are specialised cells with a tuft of beating cilia that drives waste fluid into a system of tubules, and they handle both the removal of nitrogenous waste and the balance of water in animals such as Planaria, Taenia and Fasciola.

Option B, roundworms of Aschelminthes, excrete through a simple excretory pore and renette cells, not flame cells. Option C, earthworms and the other annelids, excrete through nephridia, a pair of coiled tubules in nearly every segment. Option D, insects, excrete through Malpighian tubules opening into the gut, which is how they lose very little water. Matching the excretory structure with the phylum is a standard one-mark question, so learn the four names together: flame cells, renette cells, nephridia and Malpighian tubules, in that order of phyla.

The correct answer is B, 15 moles. The number of moles is the given mass divided by the molar mass, so 60 grams of helium divided by 4 grams per mole gives 15 moles. Helium has an atomic mass of 4, and because it is a noble gas its molecules are single atoms, so its molar mass is 4 grams and not 8. Each of those 15 moles holds 6.022 into 10 to the power 23 atoms, and at standard temperature and pressure the sample would fill about 336 litres, since one mole of any gas takes 22.4 litres. A is wrong because 12 moles uses 5 grams per mole and borrows the 12 of carbon. C is wrong because 10 moles would need a molar mass of 6, which helium does not have. D is wrong because 25 moles would need a molar mass of 2.4, the mass of no element. Exam tip: moles equal mass in grams divided by molar mass, so 4 grams of helium is exactly one mole.

The correct answer is B. Malaria is caused by the protozoan parasite Plasmodium, of which several species infect human beings, and it is transmitted by the bite of an infected female Anopheles mosquito, the male feeding on plant juices. Option A is wrong because Aedes aegypti carries the viral diseases dengue, chikungunya, yellow fever and Zika, and this pairing is the commonest confusion in the chapter. Option C is wrong because the rat flea carries plague, caused by the bacterium Yersinia pestis. Option D is wrong because no fungus causes malaria; waterborne diseases spread that way are cholera, typhoid and amoebic dysentery. Ronald Ross, working in India, showed the role of the mosquito in the spread of malaria. Prevention rests on destroying breeding places of mosquitoes, using nets and treating patients early, since the parasite completes part of its life cycle in the mosquito and part in the human liver and red blood cells.

The correct answer is D, stomata. The tiny pores on the surface of a leaf, found mostly on its lower side, are called stomata.

Each stoma is a slit guarded by two bean shaped guard cells, which swell to open it and shrink to close it. Through these pores the plant takes in carbon dioxide for photosynthesis and gives out oxygen, and water vapour escapes through them in the process called transpiration. Having them on the shaded lower surface reduces the loss of water. Floating plants such as the water lily carry their stomata on the upper surface instead, and fully submerged plants have almost none.

A is wrong: pore is only the general word for an opening and is not the botanical term. B is wrong: opening is likewise a plain description, not a name. C is wrong: cilia are tiny hair like structures that help some cells and organisms move, and they are not found on leaves.

Exam tip: stomata are leaf pores guarded by guard cells, mostly on the lower surface, used for gas exchange and for transpiration.

The correct answer is B, Ion-exchange. An ion-exchange resin or zeolite swaps the calcium and magnesium ions that cause permanent hardness for sodium or hydrogen ions.

Permanent hardness comes from the chlorides and sulphates of calcium and magnesium, which do not break down on heating. In the zeolite (permutit) process, sodium aluminium silicate takes up Ca2+ and Mg2+ and gives out Na+, which does not harden water; the exhausted zeolite is renewed by washing it with brine. Synthetic resins work the same way. Washing soda and Calgon also remove permanent hardness.

A is wrong: boiling removes only temporary hardness, by turning soluble bicarbonates into insoluble carbonates.

C is wrong: lime treatment, Clark's method, also removes only temporary (bicarbonate) hardness.

D is wrong: bubbling sulphur dioxide only makes the water acidic; it does not take out calcium or magnesium.

Exam tip: temporary hardness = bicarbonates, removed by boiling or Clark's lime; permanent = chlorides and sulphates, removed by washing soda, Calgon or ion exchange.

The correct answer is A, 1 and 4. Hooke's law holds only as far as the limit of proportionality, and that limit is either equal to or lower than the elastic limit, so statements 1 and 4 are the correct pair. Hooke's law says stress is proportional to strain, which is the straight part of the stress-strain graph; the point where the curve leaves the straight line is the limit of proportionality. A little beyond it the material still springs back to its original shape, and the last point at which it does so is the elastic limit. For most metals the two points lie very close together and for an ideal material they coincide. B is wrong because statement 2 extends the law past the straight part of the graph, where stress and strain are no longer proportional. C and D are wrong because statement 3 says always less, while the two limits may also be equal. Exam tip: order the four points as proportionality limit, elastic limit, yield point, ultimate stress.

The correct answer is B, Active transport of ions and small molecules across cell membrane against concentration gradient requires energy. Moving a substance from low to high concentration is uphill work, and the cell pays for it with ATP.

In active transport, carrier proteins called pumps in the membrane use energy from ATP to push ions such as K+ and nitrate into root hair cells, even when the soil holds far less of them than the cell does. Diffusion and osmosis, by contrast, are passive: substances move down their own gradient, from high to low concentration, without spending energy.

A is wrong: diffusion is passive and needs no energy from the cell.

C is wrong: moving anything against a concentration gradient always needs energy; the cell cannot do it for free.

D is wrong: plant cells do move ions across membranes all the time, through channels, carriers and pumps; that is how roots take up minerals.

Exam tip: down the gradient = diffusion or osmosis, no energy; up the gradient = active transport, needs ATP.

The correct answer is C, 2 s. A simple pendulum about one metre long completes one full swing in roughly two seconds, and a pendulum of this length is called the seconds pendulum. The time period of a simple pendulum is T = 2 pi times the square root of L divided by g, where L is the length of the thread and g is the acceleration due to gravity, about 9.8 metres per second squared. Putting L = 1 metre gives T = 2 x 3.14 x the square root of 1 divided by 9.8, which comes to about 2.01 seconds. The period depends only on the length and on g, not on the mass of the bob or on how far it is pulled aside, so long as the swing is small. A is wrong because a 6 second period needs a thread about 9 metres long. B is wrong because a 4 second period needs a thread about 4 metres long. D is wrong because a 1 second period belongs to a thread of only about 25 centimetres. Exam tip: the period doubles only when the length becomes four times.

The correct answer is A, Silica, sodium carbonate, borax, alumina and cullets. Glass is made by melting silica sand with fluxes and stabilisers, and this option lists the standard batch.

Silica, from pure sand, forms the glassy network. Sodium carbonate, or soda ash, lowers the melting point of silica from about 1700 °C to a workable level. Borax adds boron, which gives heat-resistant borosilicate glass such as Pyrex, and alumina makes the glass tougher and more durable. Cullet is broken waste glass fed back into the furnace; it melts easily, saves fuel and is a simple form of recycling. Ordinary soda-lime glass also uses limestone.

B is wrong: iron oxide only tints glass green or brown, and lead and sodium bicarbonate are not main ingredients.

C is wrong: it lacks the soda flux, without which silica would need far too much heat to melt.

D is wrong: metallic sodium is never used, and iron oxide is an impurity or colouring agent, not a main ingredient.

Exam tip: glass = silica (sand) + soda ash + limestone, with borax for heat-proof glass and cullet to save fuel.

The correct answer is A, The ring has higher kinetic energy. Rotational kinetic energy is ½Iω², and the ring has the larger moment of inertia.

For a thin ring about the axis through its centre and perpendicular to its plane, all the mass sits at distance R, so I = MR². For a uniform disc, much of the mass lies closer to the axis, so I = ½MR². At the same angular velocity ω, the ring has KE = ½MR²ω² while the disc has only ¼MR²ω². The ring therefore carries twice the rotational kinetic energy of the disc. The farther mass lies from the axis, the harder a body is to spin and the more energy it stores.

B is wrong: the disc has the smaller moment of inertia, so it has less energy at the same ω.

C is wrong: equal mass and radius do not mean equal moment of inertia; mass distribution matters.

D is wrong: a spinning body has rotational kinetic energy even when its centre of mass is at rest.

Exam tip: ring I = MR², disc I = ½MR², solid sphere I = ⅖MR²; rotational KE = ½Iω².

The correct answer is D, castor, which is the host of the eri silkworm and has nothing to do with lac culture. Options A, B and C are all genuine lac hosts: Palas, Kusum and Ber are the three chief host trees on whose tender twigs the lac insect is inoculated. Kusum carries the Kusmi strain, which gives the Aghani and Jethwi crops, while Palas and Ber carry the Rangeeni strain, which gives the Katki and Baisakhi crops, so four lac crops are taken over two years. India is the world's largest producer of lac and Jharkhand the leading state, and the research institute at Namkum near Ranchi, founded in 1924 as the Indian Lac Research Institute, now works as the Indian Institute of Natural Resins and Gums.

The correct answer is A, T will be slightly greater than T₀. The formula T₀ = 2π√(L/g) holds only for small swings; at large amplitudes the period grows.

The small-angle formula assumes sin θ ≈ θ. For larger angles the restoring force mg sin θ is less than mgθ, so the bob is pulled back a little more weakly and takes longer to complete each swing. A good approximation is T ≈ T₀(1 + θ²/16), with θ in radians. At 60° (about 1.05 rad) this gives a period roughly 7% longer than T₀, so the swing is noticeably but only slightly slower.

B is wrong: the weaker restoring force can only lengthen the period, never shorten it.

C is wrong: T equals T₀ exactly only in the limit of very small amplitude, not at 60°.

D is wrong: the mass of the bob cancels out in the equation of motion, at any amplitude.

Exam tip: simple pendulum period is independent of mass always, and independent of amplitude only for small swings.