DAV Public School
Class 10 Assessments
teacher
Science001
Subject: Science · Kind: chapter · Level: easy · Source: AI · 100 questions · published
Chapters: Chemical Reactions and Equations, Acids, Bases and Salts, Metals and Non-metals, Carbon and its Compounds, Periodic Classification of Elements, Life Processes, Control and Coordination, How do Organisms Reproduce?, Heredity, Light – Reflection and Refraction, The Human Eye and the Colourful World, Electricity, Magnetic Effects of Electric Current
When a cleaned magnesium ribbon burns in air with a dazzling white flame, the white powder formed is
Explanation: Magnesium combines with oxygen of the air to form a white powder of magnesium oxide, MgO.
In the balanced equation 3Fe + 4H2O → Fe3O4 + xH2, the value of x is
Explanation: 4 H2O contain 8 hydrogen atoms, so 4 molecules of H2 are needed on the right-hand side to balance hydrogen.
In a chemical equation, the symbol used for a substance present as a solution in water is
Explanation: The notation (aq) stands for aqueous, that is, the substance is dissolved in water; (g), (l) and (s) denote gaseous, liquid and solid states.
The reaction of quick lime with water to form slaked lime, CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat, is a
Explanation: Two reactants combine to form a single product, so it is a combination reaction, and heat is released, so it is exothermic.
On heating limestone (calcium carbonate) strongly, the products formed are
Explanation: Thermal decomposition of CaCO3 gives quick lime (CaO) and carbon dioxide: CaCO3(s) → CaO(s) + CO2(g).
Assertion (A): Mg + O2 → MgO is a skeletal chemical equation.
Reason (R): A skeletal chemical equation has the same number of atoms of each element on both sides of the arrow.
Explanation: The equation is unbalanced (2 oxygen atoms on the left, 1 on the right), so it is a skeletal equation; a skeletal equation does not have equal numbers of atoms on both sides, so R is false.
The reaction taking place in this experiment is best described as a
Explanation: One reactant (FeSO4) breaks down into simpler products on heating, so it is a thermal decomposition reaction.
The shiny layer formed on the walls is of
Explanation: Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l); calcium carbonate gives the shiny finish and is also the chemical formula of marble.
The gas evolved when zinc granules react with dilute sulphuric acid is
Explanation: A metal displaces hydrogen from an acid, so zinc and dilute H2SO4 give zinc sulphate and hydrogen gas.
Assertion (A): Dry HCl gas does not change the colour of dry blue litmus paper.
Reason (R): Hydrogen ions are produced from HCl only in the presence of water.
Explanation: Separation of H+ ions from HCl cannot occur without water, so dry HCl gas shows no acidic behaviour with dry litmus.
A few drops of phenolphthalein solution are added to dilute sodium hydroxide solution. The colour of the solution becomes
Explanation: Phenolphthalein is a synthetic indicator that turns pink in a basic solution such as NaOH, and the pink colour disappears when an acid is added.
The reaction between an acid and a base to give a salt and water is known as a
Explanation: In a neutralisation reaction, the effect of a base is cancelled by an acid and vice versa: Base + Acid → Salt + Water.
Dilute HCl is added to sodium carbonate and the gas evolved is passed through lime water, which turns milky. The gas evolved is
Explanation: Metal carbonates react with acids to give a salt, water and carbon dioxide, and CO2 reacts with lime water to form a white precipitate of CaCO3.
A base that dissolves in water is called a(n)
Explanation: Bases that are soluble in water are called alkalis. NaOH and KOH are examples, and they produce OH⁻ ions in water.
Assertion (A): Copper oxide dissolves in dilute hydrochloric acid to form a blue-green solution.
Reason (R): Metallic oxides are acidic in nature.
Explanation: Copper oxide reacts with dilute HCl to form copper(II) chloride, which is blue-green, so A is true. Metallic oxides react with acids to give salt and water, so they are basic, not acidic; R is false.
Which statement correctly explains the observation and the safe procedure?
Explanation: Dissolving an acid or a base in water releases a lot of heat. The acid is therefore added slowly to water with stirring, because adding water to the acid may make the mixture splash out and cause burns.
Sodium and potassium are kept immersed in kerosene oil because they
Explanation: Sodium and potassium react so vigorously with oxygen that they catch fire in the open. Keeping them in kerosene prevents accidental fires.
Which of the following is the most ductile metal?
Explanation: Ductility is the ability of a metal to be drawn into thin wires, and gold is the most ductile metal. A wire about 2 km long can be drawn from one gram of gold.
Metal oxides that react with both acids and bases to produce salts and water are called
Explanation: Oxides such as aluminium oxide and zinc oxide show both acidic and basic behaviour. Such oxides are called amphoteric oxides.
Which of the following non-metals, an allotrope of carbon, is a good conductor of electricity?
Explanation: Non-metals are generally poor conductors, but graphite, an allotrope of carbon, conducts electricity.
Which of the following metals exists as a liquid at room temperature?
Explanation: All metals except mercury are solids at room temperature. Gallium has a low melting point but still stays solid unless it is warmed on the palm.
Assertion (A): Calcium starts floating when it reacts with water.
Reason (R): Bubbles of hydrogen gas formed in the reaction stick to the surface of the metal.
Explanation: Hydrogen bubbles formed in Ca + 2H2O → Ca(OH)2 + H2 stick to the calcium and make it float. So R correctly explains A.
Which metal was most probably present in the tube with the fastest bubbling and the highest temperature rise?
Explanation: The reactivity with dilute acids decreases in the order Mg > Al > Zn > Fe. Magnesium therefore gives the fastest and most exothermic reaction.
Which of the following non-metals is lustrous?
Explanation: Iodine is a non-metal that is lustrous, which is one of the exceptions to the general properties of non-metals. Sulphur is dull, oxygen is a gas and bromine is a liquid.
Two nitrogen atoms in a molecule of nitrogen (N2) are joined by a
Explanation: Each nitrogen atom contributes three electrons to complete its octet. This gives three shared pairs, which form a triple bond.
The unique ability of carbon atoms to form bonds with other carbon atoms, giving rise to large molecules, is called
Explanation: Catenation is the property of carbon atoms linking to one another to form long chains, branched chains and rings.
Assertion (A): Carbon compounds in which the carbon atoms are linked only by single bonds are called saturated compounds.
Reason (R): Ethene (C2H4) is a saturated compound because it contains a double bond between its carbon atoms.
Explanation: Compounds with only single C–C bonds are saturated, so A is true. Ethene has a C=C double bond, so it is unsaturated and R is false.
The low melting and boiling points and the non-conducting nature of X are best explained by saying that X is
Explanation: Covalent compounds have strong bonds within molecules but weak intermolecular forces, so their melting and boiling points are low. No ions are formed, so they do not conduct electricity.
Friedrich Wöhler disproved the 'vital force' theory in 1828 by preparing which organic compound from ammonium cyanate?
Explanation: Wöhler prepared urea from ammonium cyanate, which showed that organic compounds can be made in the laboratory without a living system.
The first fullerene to be identified, C-60, has carbon atoms arranged in the shape of a
Explanation: C-60 has its carbon atoms arranged like a football. It was named fullerene because it resembles the geodesic dome designed by Buckminster Fuller.
Carbon forms four covalent bonds with hydrogen atoms in methane (CH4) because a carbon atom has
Explanation: Carbon has four valence electrons, so it is tetravalent and shares them with four hydrogen atoms to attain noble gas configuration.
In diamond, each carbon atom is bonded to
Explanation: In diamond each carbon atom is bonded to four other carbon atoms, giving a rigid three-dimensional structure; three bonds in a plane is the case for graphite.
In a Döbereiner triad, the atomic mass of the middle element is approximately
Explanation: Döbereiner found that when three elements with similar properties are arranged in order of increasing atomic mass, the middle one has an atomic mass roughly equal to the mean of the other two.
Newlands' Law of Octaves states that every eighth element, starting from a given element, has properties similar to the first, just like the
Explanation: Newlands compared the repetition of properties at every eighth element to the eighth note of a musical scale, which repeats the first note.
Mendeleev's Periodic Table was based on the arrangement of elements in increasing order of their
Explanation: Mendeleev's periodic law stated that the properties of elements are a periodic function of their atomic masses.
Mendeleev left a gap for an undiscovered element and named it eka-aluminium. The element was later discovered and named
Explanation: Eka-aluminium predicted by Mendeleev was later discovered as gallium, with properties close to his predictions.
In the Modern Periodic Table, the elements are arranged in order of increasing
Explanation: The Modern Periodic Law states that properties of elements are a periodic function of their atomic number.
Assertion (A): All elements in a group of the Modern Periodic Table have the same number of valence electrons.
Reason (R): All elements in a group have the same number of shells.
Explanation: Elements in a group have the same number of valence electrons, so A is true; but the number of shells increases down a group, so R is false.
The element X is placed in
Explanation: X has three shells, so it is in Period 3, and six valence electrons place it in Group 16.
On moving down a group in the Modern Periodic Table, the metallic character of elements
Explanation: Down a group the atomic size increases, so atoms lose electrons more easily and metallic character increases.
Organisms such as green plants, which obtain carbon dioxide and water from inorganic sources and make their own food, are called
Explanation: Autotrophs, which include green plants and some bacteria, use simple inorganic substances (carbon dioxide and water) to make their food.
The opening and closing of the stomatal pore is controlled by the
Explanation: Guard cells swell when water flows into them and open the pore; they shrink and close it.
Amoeba takes in its food by
Explanation: Amoeba forms temporary finger-like extensions that fuse over the food particle and form a food-vacuole.
In plants, the carbohydrates that are not used immediately are stored in the form of
Explanation: Plants store unused carbohydrates as starch, which acts as the internal energy reserve; glycogen is the storage form in animals.
Which of the following organisms breaks down food outside its body and then absorbs it?
Explanation: Fungi such as bread moulds, yeast and mushrooms break down food material outside the body and then absorb it.
Assertion (A): In green plants, carbohydrates not used immediately are stored as starch.
Reason (R): Plants store their surplus energy in the form of glycogen.
Explanation: Plants store surplus carbohydrates as starch, so A is true; glycogen is the storage form in our body, so R is false.
After the iodine test, which part of the leaf will show a blue-black colour, and why?
Explanation: Chlorophyll is essential for photosynthesis, so only the green areas made starch, which turns blue-black with iodine.
What result is expected, and what does it show?
Explanation: Potassium hydroxide removes carbon dioxide from jar A, so its leaf makes little or no starch, whereas the leaf of plant B does; this shows carbon dioxide is necessary for photosynthesis.
The gap between the end of the axon of one neuron and the dendrite of the next neuron is called the
Explanation: At the end of the axon, chemicals are released that cross the gap, called the synapse, and start an impulse in the next neuron.
Assertion (A): The cerebellum controls involuntary actions such as blood pressure, salivation and vomiting.
Reason (R): The medulla in the hind-brain controls these involuntary actions.
Explanation: Blood pressure, salivation and vomiting are controlled by the medulla, so R is true. The cerebellum maintains posture and balance and gives precision to voluntary actions, so A is false.
In humans, reflex arcs are formed mainly in the
Explanation: Nerves from all over the body meet in the spinal cord, so reflex arcs are formed there. This lets the response happen quickly without waiting for the brain to think.
The receptors in the tongue that detect taste are called
Explanation: Gustatory receptors detect taste, while olfactory receptors in the nose detect smell.
The spinal cord is protected by the
Explanation: The vertebral column, or backbone, protects the spinal cord. The brain is protected by the bony skull and the fluid-filled balloon inside it.
Riya's hand was withdrawn so quickly because the response was a reflex action in which
Explanation: In a reflex arc, the input nerve is connected to the output nerve in the spinal cord. This avoids the slower thinking process of the brain, so the response is fast.
Assertion (A): Muscle cells shorten when a nerve impulse reaches them.
Reason (R): Muscle cells have special proteins that change their shape and arrangement in response to nervous electrical impulses.
Explanation: On receiving an electrical impulse, the special proteins in muscle cells change shape and arrangement. This gives the cells a shorter form, which is how the muscle moves.
The main thinking part of the human brain is the
Explanation: The fore-brain is the main thinking part of the brain. It receives sensory impulses and has areas of association where the information is interpreted.
The malarial parasite, Plasmodium, reproduces by dividing into many daughter cells simultaneously. This process is called
Explanation: Plasmodium divides into many daughter cells at the same time by multiple fission. In binary fission a cell splits into only two.
Spirogyra, a multi-cellular alga with simple body organisation, reproduces when it breaks up into smaller pieces that grow into new individuals. This is called
Explanation: Spirogyra simply breaks into pieces on maturity, and each fragment grows into a new filament. This mode of reproduction is called fragmentation.
In bread mould (Rhizopus), the tiny blob-like structures called sporangia contain
Explanation: Sporangia contain spores, which can develop into new Rhizopus individuals. The thread-like hyphae are not reproductive parts.
One advantage of growing plants such as banana, orange, rose and jasmine by vegetative propagation is that
Explanation: Vegetative propagation makes it possible to grow plants like banana, orange, rose and jasmine that have lost the capacity to produce seeds. The new plants are also genetically similar to the parent.
Simple animals like Planaria, when cut into several pieces, grow each piece into a complete organism. This process is called
Explanation: Regeneration is the ability of fully differentiated organisms such as Hydra and Planaria to give rise to new individuals from cut body parts. It is carried out by specialised cells that proliferate and form the various tissues.
Assertion (A): Variation is useful for the survival of a species over time.
Reason (R): If the niche of a population changes drastically, some variants present in the population may survive.
Explanation: When a niche changes (for example, a rise in temperature), the population could be wiped out, but individuals with suitable variations can survive and grow further. This is why variation helps the species survive.
The survival of these few bacteria is best explained by the fact that
Explanation: DNA copying produces small variations, so a few bacteria were already heat-resistant. When the niche changed, these variants survived and multiplied.
In tissue culture, the small group of cells formed when cells from the growing tip of a plant divide in an artificial medium is called
Explanation: In tissue culture, cells divide rapidly in an artificial medium to form a small group of cells called a callus. The callus is then moved to a medium containing hormones for growth and differentiation.
When F1 tall pea plants (Tt) are self-pollinated, the F2 generation has the combination of TT, Tt and tt in the ratio
Explanation: Each Tt parent gives T or t gametes in equal numbers, so the F2 plants are TT, Tt and tt in the ratio 1:2:1. This gives three tall plants to one short plant.
Besides the sex chromosomes, the number of pairs of chromosomes in human beings, each with a maternal and a paternal copy, is
Explanation: Most human chromosomes occur as maternal and paternal pairs, and there are 22 such pairs. The remaining pair is the sex chromosomes.
Assertion (A): In human beings, women have a mismatched pair of sex chromosomes, XY.
Reason (R): Men have one normal-sized X chromosome and a short Y chromosome.
Explanation: Women have a perfect pair of sex chromosomes, XX, so A is false. Men have a mismatched pair with one X and one short Y, so R is true.
Which of the following F2 plants shows a new combination of traits?
Explanation: Tall/short and round/wrinkled are inherited independently, so F2 plants can be tall with wrinkled seeds or short with round seeds. The first two options are parental combinations, and there are no medium-height plants.
A section of DNA that provides the information for making one protein is called a
Explanation: A gene is the section of DNA that carries the information for one protein. Genes control characteristics or traits through the proteins they code for.
In a few reptiles, whether the developing animal becomes male or female is determined by
Explanation: In some animals such as a few reptiles, sex is decided by environmental cues. The temperature at which the fertilised eggs are kept determines the sex.
When Mendel crossed a pure tall pea plant with a pure short pea plant, all the F1 plants were tall. This shows that tallness is a(n)
Explanation: Only one parental trait (tallness) appeared in F1 and no medium-height plants were seen, so tallness is the dominant trait and shortness is recessive.
Mendel was the first scientist to arrive at the laws of inheritance because he
Explanation: Mendel combined science and mathematics and counted the individuals exhibiting a trait in every generation, which helped him arrive at the laws of inheritance.
The image formed by a plane mirror is always
Explanation: A plane mirror forms a virtual and erect image equal in size to the object, as far behind the mirror as the object is in front.
The centre of curvature of a concave mirror lies
Explanation: The centre of curvature is not a part of the mirror; it lies in front of a concave mirror and behind a convex mirror.
The radius of curvature of a convex mirror is 32 cm. Its focal length is
Explanation: For a spherical mirror R = 2f, so f = 32/2 = 16 cm, and it is positive for a convex mirror.
The diameter of the reflecting surface of a spherical mirror is called its
Explanation: The diameter of the reflecting surface of a spherical mirror is its aperture.
Assertion (A): A sheet of paper held at the focus of a concave mirror facing the Sun begins to burn.
Reason (R): A concave mirror converges the parallel rays of sunlight at its principal focus.
Explanation: The concave mirror converges sunlight to a bright spot at its principal focus, and the concentrated heat ignites the paper.
Where is the screen placed and what is the nature of the image?
Explanation: With u = –25 cm and f = –15 cm, 1/v = 1/f – 1/u gives v = –37.5 cm, so the image is real, inverted and enlarged, formed in front of the mirror.
The principal axis of a spherical mirror is a straight line that
Explanation: The principal axis is the line through the pole and the centre of curvature, and it is normal to the mirror at the pole.
In the human eye, most of the refraction of light entering the eye takes place at the
Explanation: Most refraction occurs at the outer surface of the cornea, while the crystalline lens only provides the finer adjustment of focal length.
A person with hypermetropia can see distant objects clearly but not nearby objects. The defect is corrected by using
Explanation: In hypermetropia the image of a nearby object forms behind the retina. A convex (converging) lens gives the extra focussing power needed to bring the image onto the retina.
The dark muscular diaphragm behind the cornea that controls the size of the pupil is called the
Explanation: The iris is a dark muscular diaphragm that controls the size of the pupil, and so regulates the amount of light entering the eye.
In refraction through a triangular glass prism, the angle between the emergent ray and the incident ray is called the
Explanation: Because of the peculiar shape of the prism, the emergent ray bends at an angle to the incident ray. This angle is called the angle of deviation.
Assertion (A): When we look at nearby objects, the focal length of the eye lens decreases.
Reason (R): The ciliary muscles contract, which increases the curvature of the eye lens and makes it thicker.
Explanation: For nearby objects the ciliary muscles contract, so the lens becomes thicker with greater curvature. A thicker lens has a shorter focal length, so R explains A.
Which defect of vision does Ravi have, and which lens will correct it?
Explanation: His near point is farther than 25 cm and the image of a close object forms behind the retina. This is hypermetropia, which a convex lens corrects.
A rainbow is seen in the sky after a rain shower. It is always formed in a direction
Explanation: A rainbow forms when sunlight is dispersed and internally reflected by water droplets. It is always seen in the direction opposite to the Sun.
The SI unit of electrical resistivity of a material is
Explanation: From R = ρl/A, resistivity ρ = RA/l. Its unit is therefore Ω × m²/m = Ω m.
How much work is done in moving a charge of 5 C across two points having a potential difference of 6 V?
Explanation: Work done W = V × Q = 6 V × 5 C = 30 J.
Assertion (A): An ammeter is always connected in series in a circuit.
Reason (R): A voltmeter is always connected in parallel across the points between which the potential difference is to be measured.
Explanation: An ammeter is connected in series and a voltmeter in parallel, so both statements are true. However, the way a voltmeter is connected does not explain why an ammeter is connected in series.
What will the ammeter reading be with the longer wire?
Explanation: Resistance is directly proportional to length, so doubling the length doubles the resistance. By I = V/R the current halves to 0.2 A.
The SI unit of electric charge is
Explanation: The SI unit of electric charge is the coulomb (C); one coulomb is the charge contained in nearly 6 × 10^18 electrons.
A current of 0.5 A flows through a bulb filament for 10 minutes. The charge that flows through the circuit is
Explanation: Q = It = 0.5 A × 600 s = 300 C.
According to Ohm's law, the potential difference across the ends of a metallic wire is directly proportional to the current through it, provided the
Explanation: Ohm's law holds for a given metallic wire only when its temperature remains the same, so that V/I = R is constant.
The direction of the magnetic field lines outside a bar magnet is
Explanation: By convention, field lines emerge from the north pole and merge at the south pole outside the magnet.
The discovery that a compass needle gets deflected by a current-carrying wire was made in 1820 by
Explanation: Hans Christian Oersted accidentally discovered in 1820 that a current-carrying wire deflects a nearby compass needle.
The pattern of magnetic field lines around a straight wire carrying current is
Explanation: Iron filings around a straight current-carrying wire align in concentric circles, representing the field lines.
The magnetic field produced by a straight current-carrying wire at a point
Explanation: The field produced by a given current decreases as the distance from the wire increases, so the compass deflection falls.
In the household wiring, the earth wire has green insulation and is used mainly
Explanation: The earth wire is connected deep inside the earth as a safety measure so leakage of current to a metallic body does not give a severe shock.
Assertion (A): No two magnetic field lines cross each other.
Reason (R): At a point of intersection, a compass needle would have to point in two directions, which is not possible.
Explanation: Field lines never intersect because the field has one direction at each point; a crossing would give the needle two directions.
What happens to the magnetic field at the centre of the 10-turn coil compared with a single loop?
Explanation: The current in each turn has the same direction, so the fields add up and a coil of n turns gives n times the field of a single turn.