General Science Previous Year Questions (PYQ) with Answers – Page 4

The correct answer is B, the same, opposite. The same magnet moves at the same speed in both cases, so the rate of change of magnetic flux through the coil is equal and the induced potential difference has the same magnitude. But turning the other pole towards the coil reverses the direction of the field through it, so the induced voltage takes the opposite sign. This follows from Faraday's law of electromagnetic induction, which says the induced emf equals the rate of change of flux, and from Lenz's law, which fixes the direction so that the induced current opposes the change causing it. A is wrong because the sign must flip once the pole facing the coil is reversed. C is wrong because the speed, and therefore the rate of flux change, is unchanged, so the two magnitudes match. D is wrong on both counts. Exam tip: speed decides how big the induced emf is, the field direction decides its sign - Faraday for magnitude, Lenz for direction.

The correct answer is A, Peacock. The peacock is a bird, and all birds, like mammals, have a heart of four chambers: two atria and two ventricles. Four chambers keep oxygen-rich blood and oxygen-poor blood completely apart, so the body gets fully oxygenated blood. Birds and mammals need this because they are warm-blooded and burn a great deal of energy to hold a steady body temperature; flight makes the demand greater still. Crocodiles are the only reptiles with a four-chambered heart. B is wrong because a sea horse is a fish and has a two-chambered heart, one atrium and one ventricle. C is wrong because a frog, being an amphibian, has three chambers, two atria and a single ventricle in which the two kinds of blood mix. D is wrong for the same reason as the sea horse. Exam tip: fish 2 chambers, amphibians and most reptiles 3, birds and mammals 4; the peacock is India's national bird.

The correct answer is C, Zn. Zinc has atomic number 30, which means each of its atoms carries 30 protons in the nucleus. In the modern periodic table the elements are arranged in increasing order of atomic number, as Moseley showed, and zinc sits in group 12 of the fourth period at the end of the first transition series. It is a bluish-white metal that is used to galvanise iron against rust, in dry cells and in brass, an alloy of copper and zinc. A is wrong because nickel (Ni) has atomic number 28. B is wrong because iron (Fe) has atomic number 26 and is the most used metal in the world. D is wrong because cobalt (Co) has atomic number 27 and is the metal at the centre of vitamin B12. Exam tip: learn the run 24 to 30 in order — Cr, Mn, Fe, Co, Ni, Cu, Zn.

The correct answer is A, Archimedes' Principle. It states that the upthrust on a body dipped fully or partly in a fluid equals the weight of the fluid the body pushes aside. This is why a bucket of water feels lighter while it is still in the well, and why a ship of steel floats: its hollow shape displaces enough water to balance its own weight. The principle also gives the law of flotation and is used to find the purity of metals and the density of liquids with a hydrometer. B is wrong because Bernoulli's principle links the speed of a flowing fluid with its pressure, and explains lift on an aeroplane wing. C is wrong because the Beer–Lambert law deals with how much light a solution absorbs as it passes through. D is wrong because Pascal's law says pressure applied to an enclosed fluid is passed on equally in every direction, which is the basis of hydraulic brakes and lifts. Exam tip: Archimedes for buoyancy, Pascal for hydraulic press, Bernoulli for aerofoil lift.

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 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 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.

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 D, It has no unit. Magnification is a ratio of two lengths, so the units cancel and it is a pure number. For a mirror or a lens, magnification m equals the height of the image divided by the height of the object (h′/h). For a lens it also equals v/u, the image distance divided by the object distance, and for a mirror it equals −v/u. A value of 2 means the image is twice the size of the object; a value less than 1 means it is smaller. With the usual sign convention a negative m means a real, inverted image, and a positive m means a virtual, erect image. A is wrong because the dioptre is the unit of the power of a lens, P = 1/f with f in metres. B is wrong because the newton is the SI unit of force. C is wrong because the centimetre measures lengths such as focal length and image distance, not their ratio. Exam tip: magnification = no unit; power of a lens = dioptre; focal length = metre or centimetre.

The correct answer is A, un-deviated. A ray that passes through the optical centre of a thin lens comes out in the same direction, without any bending. The optical centre is the central point of the lens on its principal axis. Near it the two faces of the lens are almost parallel, like a thin glass slab, so the ray shifts sideways by a negligible amount and keeps its direction. This is one of the three standard rays used to draw ray diagrams: a ray parallel to the principal axis passes through the focus after refraction in a convex lens, a ray through the focus comes out parallel to the axis, and a ray through the optical centre goes straight on. B is wrong because only rays that strike the lens away from the centre are deviated. C is wrong because bent means the same as deviated, which does not happen at the centre. D is wrong because a lens refracts light; reflection is what mirrors do. Exam tip: through the optical centre = straight through; parallel ray = through the focus; ray through the focus = emerges parallel.

The correct answer is D, (i) - (c), (ii) - (b), (iii) - (a). Red cabbage is a natural acid-base indicator, methyl orange is a synthetic acid-base indicator, and onion and clove are olfactory indicators. An indicator tells whether a solution is acidic or basic. Natural indicators come from plants: litmus from lichen, turmeric, red cabbage leaves and coloured petals such as hydrangea and petunia. Synthetic indicators made in the laboratory include methyl orange, which is red in acid and yellow in base, and phenolphthalein, which is colourless in acid and pink in base. Olfactory indicators change their smell instead of their colour; onion, vanilla and clove lose their smell in a basic solution. A is wrong because it calls methyl orange an olfactory indicator. B is wrong because it labels red cabbage as olfactory. C is wrong because it puts onion and clove under natural colour indicators. Exam tip: change of smell = olfactory (onion, clove, vanilla); change of colour = litmus, turmeric, red cabbage; lab-made = methyl orange, phenolphthalein.

The correct answer is D, Hg. Mercury (Hg) belongs to group 12, not group 11. Group 11 of the modern periodic table holds copper (Cu, atomic number 29), silver (Ag, 47) and gold (Au, 79). These three are called the coinage metals because coins were made from them; each has one electron in its outermost s orbital, which makes them soft and shiny, and silver and copper are the best conductors of electricity of all metals. Mercury sits right next to gold in period 6 but in group 12, together with zinc and cadmium, and it is the only metal that is liquid at room temperature. A is wrong because silver is a group 11 metal. B is wrong because gold is also in group 11. C is wrong because copper heads group 11. Exam tip: Group 11 = Cu, Ag, Au (coinage metals); Group 12 = Zn, Cd, Hg; the liquid metal mercury is never a coinage metal.

The correct answer is A, Platelets. Platelets are the tiny cell fragments that rush to a cut and start the clot. They are also called thrombocytes and are made in the bone marrow from large cells called megakaryocytes. A healthy adult has about 1.5 to 4 lakh platelets per cubic millimetre of blood, and each one lives for only 8 to 10 days. At a wound they stick together to form a plug and release chemicals that turn the soluble protein fibrinogen into fibrin threads, which trap blood cells and seal the leak. B is wrong because plasma proteins such as fibrinogen take part in clotting, but the paper marks platelets as the component that starts and aids clot formation. C is wrong because white blood cells fight infection, not bleeding. D is wrong because red blood cells carry oxygen with haemoglobin. Exam tip: RBC = oxygen, WBC = immunity, platelets = clotting; a falling platelet count is what dengue is known for.

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 B, Potassium – Po. The symbol of potassium is K, from its Latin name kalium; Po is the symbol of polonium, the radioactive element discovered by Marie Curie in 1898 and named after Poland. Potassium has atomic number 19, sits in group 1 as an alkali metal, and is soft enough to cut with a knife. Several common elements carry symbols from Latin names rather than English ones, and examiners love them: sodium Na (natrium), iron Fe (ferrum), copper Cu (cuprum), silver Ag (argentum), gold Au (aurum), tin Sn (stannum), lead Pb (plumbum), mercury Hg (hydrargyrum) and tungsten W (wolfram). A is a correct pair because phosphorus is P, atomic number 15. C is a correct pair because iron is Fe from ferrum, atomic number 26. D is a correct pair because iodine is I, atomic number 53, a halogen. Exam tip: K is potassium and Po is polonium; when a symbol looks like the first two letters of the English name, check whether the element actually uses a Latin name.

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 B, Both I and II. Both pairs are wrong. Amyloplasts store starch, a carbohydrate, and aleuroplasts store proteins; oils and fats are stored by elaioplasts. Plastids are organelles found only in plant cells. Chloroplasts hold chlorophyll and do photosynthesis, chromoplasts hold the yellow, orange and red pigments of flowers and fruits, and leucoplasts are colourless storage plastids. The leucoplasts are named after what they keep: amyloplasts keep starch (amylum), as in potato tubers; elaioplasts keep oils (elaion means oil), as in castor seeds; aleuroplasts keep proteins (aleurone), as in the outer layer of wheat grains. A is wrong because it accepts pair II, which links aleuroplasts to carbohydrates instead of proteins. C is wrong because it treats both pairs as correct. D is wrong because it accepts pair I, which links amyloplasts to fats instead of starch. Exam tip: amylo = starch, elaio = oil, aleuro = protein; all three are leucoplasts.

The correct answer is B, 14 : 3. Ammonia is NH3, so one nitrogen atom of mass 14 is joined to three hydrogen atoms of mass 1 each, giving 14 : 3 by mass. This is the law of constant proportions given by Proust in 1799: a pure compound always contains the same elements in the same ratio by mass, whatever its source. The NCERT Class 9 chapter uses exactly these examples, water H2O with hydrogen to oxygen 1 : 8 and ammonia NH3 with nitrogen to hydrogen 14 : 3. Remember that the ratio by mass is not the ratio by atoms; by atoms ammonia is 1 : 3, by mass it is 14 : 3 because nitrogen is fourteen times heavier than hydrogen. A is wrong because 11 is not the atomic mass of nitrogen. C is wrong for the same reason, even though the hydrogen part is right. D is wrong because it counts only one hydrogen atom instead of three. Exam tip: water 1 : 8, ammonia 14 : 3, carbon dioxide 3 : 8, all by mass.

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 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.