General Science Previous Year Questions (PYQ) with Answers – Page 6

The correct answer is C, Arthropoda. The name itself says so: in Greek arthros means jointed and podos means foot, so arthropods are the animals with jointed legs. They also have a hard outer skeleton of chitin, a segmented body and an open circulatory system, and they shed the skeleton as they grow, a process called moulting. Arthropoda is the largest phylum in the animal kingdom, holding insects, spiders, scorpions, crabs, prawns, centipedes and millipedes - about eighty out of every hundred known animal species. Option A is wrong because molluscs such as snails, octopus and mussels have a soft body with a muscular foot and usually a shell. Option B is wrong because nematodes are unsegmented roundworms like Ascaris, with no legs at all. Option D is wrong because echinoderms such as starfish and sea urchins are spiny-skinned marine animals that move on tube feet. Exam tip: Arthropoda - jointed legs, chitin skeleton, largest phylum; Mollusca is the second largest.

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 A, Vitamin K. The liver needs vitamin K to make several clotting factors, including prothrombin, which help blood form a clot and seal a wound. Its letter comes from the German word ‘Koagulation’. When it is lacking, even small cuts bleed for a long time and bruises form easily. Newborn babies have very little of it, so hospitals give them a vitamin K injection at birth to prevent dangerous bleeding. Good sources are green leafy vegetables such as spinach, cabbage and fenugreek, and bacteria in our gut also make some of it. It is a fat-soluble vitamin, like A, D and E. Option B is wrong because vitamin E (tocopherol) works mainly as an antioxidant that protects cells. Option C is wrong because vitamin A (retinol) is needed for vision, and its lack causes night blindness. Option D is wrong because vitamin C (ascorbic acid) keeps gums and skin healthy; its lack causes scurvy, with bleeding gums, but it is not a clotting vitamin. Exam tip: K for Koagulation; A for night blindness, C for scurvy, D for rickets.

The correct answer is B, Vitamin K. The liver needs vitamin K to make prothrombin and other clotting factors, so without it blood takes much longer to clot. The letter K comes from the German word Koagulation, which makes it easy to remember. Vitamin K1, or phylloquinone, comes from green leafy vegetables such as spinach, and bacteria in the large intestine also make a form of it. Newborn babies have very little vitamin K, which is why they are given a vitamin K injection at birth to prevent bleeding. A lack of it causes easy bruising and bleeding that does not stop. Option A is wrong because vitamin A, retinol, is needed for vision, and its lack causes night blindness. Option C is wrong because vitamin D, calciferol, helps absorb calcium, and its lack causes rickets. Option D is wrong because the B vitamins help release energy from food, and their lack causes diseases such as beriberi and pernicious anaemia. Exam tip: K for Koagulation; A for eyes, D for bones.

The correct answer is C, Vitamin C. Milk contains very little vitamin C, and what little there is gets destroyed further when milk is boiled. Milk is otherwise called a nearly complete food: it gives calcium and phosphorus for bones and teeth, good-quality protein, mainly casein, the sugar lactose, fat, and vitamins A, B2 and B12. Its two well-known gaps are vitamin C and iron. Vitamin C, or ascorbic acid, comes from fresh fruits such as amla, guava, lemon and orange, and a lack of it causes scurvy, with bleeding gums as the classic sign. Option A is wrong because milk is one of the richest everyday sources of calcium. Option B is wrong because milk supplies good protein, which is why it is advised for growing children. Option D is wrong because milk carries a carbohydrate of its own, lactose, the milk sugar. Exam tip: milk is poor in vitamin C and iron, and rich in calcium, protein and lactose.

The correct answer is A, Candela. Luminous intensity is the amount of visible light a source sends out in a given direction per unit solid angle, and its SI base unit is the candela (cd), roughly the light of one ordinary candle. It is one of the seven SI base units: metre for length, kilogram for mass, second for time, ampere for electric current, kelvin for temperature, mole for amount of substance and candela for luminous intensity. Do not mix it up with the lumen, the unit of luminous flux (total light output), or the lux, the unit of illuminance (lumens per square metre falling on a surface). Option B is wrong because the mole measures amount of substance, 6.022 × 10²³ particles. Option C is wrong because the kelvin measures thermodynamic temperature. Option D is wrong because the ampere measures electric current. Exam tip: the seven base units in one line: m, kg, s, A, K, mol, cd; candela = intensity, lumen = flux, lux = illuminance.

The correct answer is B, Pressure. The torr is a unit of pressure named after Evangelista Torricelli, the Italian scientist who invented the mercury barometer in 1643. One torr is the pressure of a one-millimetre column of mercury, so 1 torr = 1 mm Hg, and it equals about 133.3 pascal. Normal atmospheric pressure at sea level is 760 torr, which is the same as 760 mm Hg, 1 atmosphere or 101,325 pascal. The pascal is the SI unit of pressure, one newton per square metre, but the torr and mm Hg are still used for blood pressure and vacuum work. A, Power, is measured in watt, with horsepower as the older unit. C, Energy, is measured in joule, with calorie and electron-volt as other units. D, Force, is measured in newton, or dyne in the CGS system. Exam tip: pressure units are pascal, bar, atmosphere, torr and mm Hg; 760 torr = 1 atm.

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, 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 B, Friction. Brakes work on friction: a lining is pressed against a moving drum or disc, and the rubbing force slows the wheel down. Friction is the force that opposes motion between two surfaces in contact. In a drum brake the shoes push outward against the inner face of the drum, while in a disc brake the pads grip a rotating disc from both sides; in each case the kinetic energy of the vehicle is turned into heat, which is why brakes grow hot on a long downhill run. The friction between the tyre and the road then stops the vehicle itself, so a smooth or wet road lengthens the stopping distance. Option A is wrong because vibration only shakes a body and cannot take away its energy in a controlled way. Option C is wrong because suction is a pressure difference; a vacuum booster only helps the driver press the pedal, it does not stop the wheel. Option D is wrong because dragging is not a physical principle. Exam tip: brakes turn kinetic energy into heat through friction.

The correct answer is C, Boron. Boron has three electrons in its outermost shell, so it is a trivalent element and is used as a p-type dopant. When a trivalent atom such as boron, aluminium, gallium or indium is added to silicon or germanium, it can form only three covalent bonds with its four neighbours, so one bond is left incomplete. That empty place is called a hole, it behaves like a positive charge carrier, and the doped crystal becomes a p-type semiconductor in which holes are the majority carriers. Adding a pentavalent atom instead leaves a free electron and gives an n-type semiconductor. Option A is wrong because arsenic has five valence electrons and is pentavalent. Option B is wrong because antimony is also pentavalent and is used for n-type doping. Option D is wrong because phosphorus has five valence electrons and donates an electron to the crystal. Exam tip: trivalent dopants such as boron, aluminium, gallium and indium give p-type material, while pentavalent ones such as phosphorus, arsenic and antimony give n-type.

The correct answer is A, 2. A centre-tap full wave rectifier needs two p-n junction diodes, one for each half of the input cycle. The secondary winding of the transformer is tapped at its middle, so its two halves give equal voltages of opposite sign. During one half cycle the upper diode conducts and during the next half cycle the lower diode conducts, and both send current through the load in the same direction, so the output has two pulses in every cycle. That is why a full wave rectifier gives a higher average output and a lower ripple than a half wave one. The other way to build a full wave rectifier is the bridge circuit, which uses four diodes but needs no centre tap. Option B is wrong because one diode makes a half wave rectifier that uses only half of each cycle. Option C is wrong because four diodes are used in a bridge rectifier. Option D is wrong because six diodes are used in a three-phase full wave rectifier. Exam tip: half wave 1 diode, centre-tap full wave 2, bridge 4.

The correct answer is D, 0.7 V. A silicon diode in forward bias drops about 0.7 volt across itself, whatever the supply voltage is. This value is the barrier or knee voltage of a silicon p-n junction: current begins to flow only after the applied voltage crosses about 0.7 V, and after that the drop across the diode stays near 0.7 V while the rest of the supply appears across the resistor. Here 12 V minus 0.7 V, that is 11.3 V, falls across the 240 ohm resistor and fixes the current in the circuit. A germanium diode has a lower knee voltage of about 0.3 V. Option A is wrong because 1.5 V is the voltage of a dry cell and has nothing to do with the junction. Option B is wrong because half the supply would appear across the diode only if it behaved like a resistor of the same value. Option C is wrong because the full 12 V appears across the diode only when it is reverse biased or the circuit is broken. Exam tip: silicon 0.7 V, germanium 0.3 V.

The correct answer is D, Volt. Potential difference is the work done to move a unit charge between two points, and its SI unit is the volt. V = W/Q, so 1 volt = 1 joule per coulomb. It is measured with a voltmeter, which is always connected in parallel across the part of the circuit being tested. The unit is named after Alessandro Volta, the Italian scientist who made the first electric battery, the voltaic pile. Household supply in India is 230 V, while a pencil cell gives 1.5 V. A is wrong because the ampere is the unit of electric current, measured with an ammeter joined in series. B is wrong because the tesla is the unit of magnetic field strength (magnetic flux density). C is wrong because the coulomb is the unit of electric charge; one coulomb is the charge of about 6.25 × 10¹⁸ electrons. Exam tip: Current = ampere, Charge = coulomb, Potential difference = volt, Resistance = ohm, Power = watt, Energy = joule.

The correct answer is D, 32. The N shell is the fourth shell (n = 4), and the most electrons a shell can hold is given by the formula 2n², so 2 × 4² = 32. The shells around the nucleus are named K, L, M and N for n = 1, 2, 3 and 4, and the same formula gives them room for 2, 8, 18 and 32 electrons. This is the Bohr–Bury scheme taught in Class 9. One more rule is often tested with it: the outermost shell of an atom cannot hold more than 8 electrons, which is why potassium is written 2, 8, 8, 1 and not 2, 8, 9. A is wrong because 2 is the capacity of the K shell. B is wrong because 8 is the capacity of the L shell. C is wrong because 16 is not the capacity of any shell; the M shell holds 18. Exam tip: remember 2n², so K = 2, L = 8, M = 18 and N = 32.

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 D, New Cartesian sign convention. It is the standard set of rules used for reflection by spherical mirrors and for the mirror formula. Under this convention the pole of the mirror is the origin and the principal axis is the x-axis. The object is always placed on the left, all distances are measured from the pole, distances in the direction of the incident light are positive and those against it are negative. Heights above the axis are positive and below it negative, so a concave mirror has a negative focal length and a convex mirror a positive one. A is wrong because 'system convention' is not a named rule in optics. B is wrong because 'sign convention' is only the general idea; the specific set used is the New Cartesian one. C is wrong because 'mirror convention' is not a recognised term. Exam tip: New Cartesian means measure from the pole; concave f is negative, convex f is positive; mirror formula 1/v + 1/u = 1/f.

The correct answer is B, violet light. Violet has the shortest wavelength in visible light, so glass slows it the most and bends it the most. White light is a mix of seven colours, remembered as VIBGYOR. The refractive index of glass is slightly different for each colour, highest for violet and lowest for red. So when white light passes through a prism, each colour bends through a different angle and the light spreads into a coloured band called a spectrum. This splitting is called dispersion, and Isaac Newton showed it with a glass prism in his experiments of 1666. A rainbow is the same dispersion happening inside raindrops. Option A is wrong because red has the longest wavelength and is bent the least, so it lies at the other end of the spectrum from violet. Option C is wrong because yellow lies in the middle of the spectrum and deviates less than violet. Option D is wrong because blue bends more than yellow but still a little less than violet. Exam tip: red deviates least and violet most; the shorter the wavelength, the bigger the bend.

The correct answer is A, Bauxite, Magnetite, Malachite and Calamine respectively. Each metal here is paired with one of its best-known ores. Bauxite is hydrated aluminium oxide; alumina is refined from it and then broken down by electrolysis in the Hall-Héroult process. Magnetite (Fe3O4) is the magnetic ore of iron, while haematite (Fe2O3) is India's chief iron ore. Malachite is a green basic copper carbonate, though copper pyrites is the main commercial ore of copper. Calamine is zinc carbonate (ZnCO3), and zinc blende (ZnS) is the other main ore of zinc; the Zawar mines of Rajasthan are famous for it. Option B is wrong because it gives aluminium to magnetite and iron to bauxite. Option C is wrong because it runs the list backwards, pairing aluminium with calamine and zinc with bauxite. Option D is wrong because malachite is an ore of copper, not aluminium, and bauxite is not an ore of copper. Exam tip: "B-M-M-C" in order: Bauxite-Al, Magnetite-Fe, Malachite-Cu, Calamine-Zn.

The correct answer is C, 143. The number 235 is the mass number and uranium's atomic number is 92, so the nucleus holds 235 minus 92, that is 143 neutrons. The mass number (A) counts protons and neutrons together, while the atomic number (Z) counts only protons, so neutrons = A − Z. Every uranium atom has 92 protons; its isotopes differ only in the number of neutrons. Uranium-235 makes up only about 0.7% of natural uranium, the rest being mostly U-238 with 146 neutrons. Yet U-235 is the isotope that splits easily when struck by a slow neutron, which is why reactor fuel is "enriched" in it. Option A is wrong because 235 is the total of protons and neutrons, not the neutrons alone. Option B is wrong because 92 is the number of protons, that is the atomic number. Option D is wrong because 51 has no link with this nucleus and is only a distractor. Exam tip: neutrons = mass number minus atomic number; U-235 has 143 and U-238 has 146.