CBSE Class 10 Science
Previous Year Questions

What happens when dilute hydrochloric acid is added to iron filings? Choose the correct answer: (a) Hydrogen gas and iron chloride are produced (b) Chlorine gas and iron hydroxide are produced (c) No reaction takes place (d) Iron salt and water are produced.

Balance the following chemical equation: Fe + H₂O → Fe₃O₄ + H₂

A shiny brown-coloured element 'X' on heating in air becomes black in colour. Name the element 'X' and the black-coloured compound formed.

Write balanced chemical equations for the following reactions: (i) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water (ii) Zinc + Silver nitrate → Zinc nitrate + Silver (iii) Aluminium + Copper chloride → Aluminium chloride + Copper

What is a redox reaction? When a magnesium ribbon is burnt in oxygen, it gets converted to magnesium oxide. Write the balanced chemical equation for this reaction. In this reaction identify the substance that is oxidised and the substance that is reduced.

Define combination reaction. Give one example of a combination reaction which is also an exothermic reaction.

Why should magnesium ribbon be cleaned before burning in air? Write the balanced equation for the burning of magnesium in air.

What is a decomposition reaction? Give one example each of a thermal decomposition reaction and a photolytic decomposition reaction. Write balanced chemical equations for both.

Which of the following is a double displacement reaction? (a) Pb + CuCl₂ → PbCl₂ + Cu (b) Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl (c) 2H₂ + O₂ → 2H₂O (d) 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃

Identify the type of chemical reaction taking place when: (i) Bread is toasted (ii) Milk turns sour (iii) Iron nail is placed in copper sulphate solution. Write the balanced equation for reaction (iii).

What is rancidity? Write two methods to prevent rancidity of food.

(a) Write a balanced chemical equation for the reaction taking place when lead nitrate solution is mixed with potassium iodide solution. Name the type of reaction. (b) What is observed when silver chloride is kept in sunlight? Write the balanced chemical equation and name the type of reaction.

A student adds a spoonful of washing soda to acetic acid in a test tube. List any two observations the student is likely to make.

What is pH scale? Name the acid present in the following: (i) Tomato (ii) Vinegar (iii) Tamarind

What is observed when: (i) Dry litmus paper is brought in contact with HCl gas (ii) HCl gas is dissolved in water. Give reason for your answer.

Why does tooth decay start when the pH of mouth is lower than 5.5? What role does pH play in our digestive system?

Three test tubes A, B and C contain three liquids — baking soda solution, lemon juice and tap water, respectively. A blue litmus paper is dipped in each. In which test tube/s the litmus will turn red? Give reason.

What is the common name of NaHCO₃? Explain its use in making bread and cake soft and fluffy. Write the chemical reaction involved.

What is bleaching powder? Give any two uses of bleaching powder.

What is a neutralisation reaction? Give two examples. Write balanced chemical equations for both.

On adding a few drops of universal indicator to three test tubes containing HCl, NaOH and CH₃COOH solutions respectively, what colour change will you observe? Give reason.

How is plaster of paris prepared from gypsum? Write the chemical equation. State one important property and one use of plaster of paris.

What is the chemical formula of washing soda? Describe in brief the preparation of washing soda from baking soda. Write the two uses of washing soda.

An aqueous solution turns red litmus paper blue. Excess addition of which of the following solutions would reverse this change? (a) Baking powder (b) Lime (c) Ammonium hydroxide solution (d) Hydrochloric acid

Name a metal (i) that is liquid at room temperature (ii) that can be cut with a knife (iii) that is the best conductor of heat (iv) that is a poor conductor of heat.

Write the electron dot structure of: (i) Sodium chloride (ii) Magnesium chloride. What type of bond is present in each?

What is thermite reaction? In which industry is it used? Write the balanced chemical equation for the reaction.

(a) What is an ore? (b) Why are metals like sodium and potassium kept under kerosene? (c) Name the process used to concentrate sulphide ores.

What is corrosion? State two methods to prevent corrosion of iron.

Write the steps involved in the extraction of metals of: (i) Low reactivity (ii) Medium reactivity, with examples.

What is galvanisation? Why is it done? Name the metal used for galvanisation of iron.

The following table shows the reactions of some metals: Metal | Cold water | Hot water | Steam | Dilute HCl. Based on this, arrange the metals in decreasing order of reactivity. Explain what you observe.

Which property of metals is used to make electrical wires? Name two metals that are best conductors of electricity.

Give reasons: (i) Platinum, gold and silver are used to make jewellery. (ii) Sodium and potassium are stored under kerosene. (iii) Aluminium is a highly reactive metal, yet it is used to make cookware.

What is meant by refining of metals? Describe the electrolytic refining of copper with the help of a labelled diagram.

An element forms an oxide A₂O₃ which is acidic in nature. Identify A as metal or non-metal. State how this oxide will react with (a) water (b) HCl (c) NaOH.

What is catenation? State two properties of carbon that lead to the formation of a large number of carbon compounds.

Write the IUPAC names of: (i) CH₃COCH₃ (ii) CH₃CHO (iii) HCOOH

What is saponification? Write the chemical equation for the saponification reaction and name the products formed.

A compound X of sodium is used for making bread and cake. When compound X is heated strongly, a gas Y is produced which turns lime water milky. Identify X and Y. Write the chemical equation for heating of X.

Distinguish between esterification and saponification reactions. Give one example of each with a balanced chemical equation.

What are structural isomers? Draw the structural formula of two isomers of butane (C₄H₁₀).

What are homologous series? State any two characteristics of a homologous series. Write the next two homologues of CH₃OH.

Explain why carbon forms compounds mainly by covalent bonding. Also explain why some carbon compounds are good conductors of electricity while most are not.

How is ethanol converted to ethene? Write the balanced chemical equation and state the type of reaction.

What is micelle formation? Explain the cleansing action of soap. Why are soaps not suitable for use with hard water?

The molecular formula of two carbon compounds are C₂H₆ and C₃H₈. (i) Name the compounds. (ii) Draw their electron dot structures. (iii) Are they saturated or unsaturated compounds?

Ethanol and ethanoic acid are both soluble in water. State one test to distinguish between them. Write the equation for the chemical reaction involved.

What are the raw materials required for photosynthesis? Where does each come from?

Explain the role of the following in human digestive system: (i) Saliva (ii) Bile (iii) Villi

What is the significance of emulsification of fats? Name the organ that produces bile and the organ that stores it.

Draw a diagram of the human heart and label the following parts: left ventricle, right atrium, aorta, pulmonary artery.

What is double circulation? Why is it necessary in human beings?

How are the alveoli designed to maximise exchange of gases? Explain.

Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their (i) Structure (ii) Function.

What is osmoregulation? Name the organ responsible for it in humans. What would happen if the kidneys stop functioning?

Describe the process of nutrition in Amoeba with a labelled diagram.

What are the differences between aerobic and anaerobic respiration? Give one example of an organism that uses anaerobic respiration.

What are stomata? Write two functions of stomata. Draw a well-labelled diagram of stomata.

Explain the mechanism of transportation of water and minerals in plants. What is the role of transpiration in this process?

What is a reflex action? Explain with an example. Draw a labelled diagram showing the reflex arc.

Name the hormone secreted by: (i) Pancreas (ii) Thyroid gland (iii) Adrenal gland (iv) Pituitary gland. State one function of each.

What happens at the synapse between two neurons? Explain the role of synapse in the neural coordination.

How do auxins promote the growth of a tendril around a support? Explain with a diagram.

What is iodised salt? Why is the use of iodised salt advisable? Name the disease caused by deficiency of iodine and state its symptoms.

Distinguish between voluntary and involuntary actions. Give one example of each. Which part of the brain controls involuntary actions?

What are tropic movements in plants? Explain phototropism with the help of a diagram.

Draw the structure of a neuron and label the following: dendrite, cell body, axon, nerve ending.

What is the role of the brain in reflex action? Name the part of the brain that: (i) Controls posture and balance (ii) Controls thinking.

Why are endocrine glands called ductless glands? Name two endocrine glands and write the hormone secreted by each and its function.

What is geotropism? Give an example. How does the plant show geotropic response?

What is the difference between binary fission and multiple fission? Give one example of each.

List two advantages of vegetative propagation. Write any two methods of artificial vegetative propagation with one example each.

Draw a labelled diagram of the longitudinal section of a flower. Name the male and female reproductive parts of the flower.

What is pollination? Distinguish between self-pollination and cross-pollination.

Explain the process of budding in Hydra with the help of a diagram. Why is it considered asexual reproduction?

What are contraceptives? List two mechanical and two chemical methods of contraception. State one advantage of using contraceptive methods.

Explain the following terms with one example each: (i) Fragmentation (ii) Regeneration (iii) Spore formation.

Draw a diagram of human male reproductive system and label: testis, vas deferens, urethra, seminal vesicle.

What changes are observed in girls at puberty? Name the hormone responsible for these changes.

Describe in brief what happens in the human female reproductive system after fertilisation.

Why does menstruation occur? What happens if the egg gets fertilised? Explain the role of the placenta.

In a cross between a tall pea plant (TT) and a short pea plant (tt), what will be the phenotype and genotype of the F₁ generation? What will be the ratio of tall to short plants in the F₂ generation?

A human male has 23 pairs of chromosomes. State the number of chromosomes in (i) a sperm (ii) an egg (iii) a zygote. How is the sex of a child determined in human beings?

What are fossils? How is the age of fossils determined? What information do fossils provide us?

Explain the terms: (i) Dominant trait (ii) Recessive trait (iii) Alleles. Give one example for each.

What are analogous and homologous organs? Give one example of each. What do they indicate about evolution?

"Variations that confer advantage are more likely to survive in a population." Justify this statement with an example.

In Mendel's experiment, when he crossed tall pea plants with dwarf pea plants, he found that in F₂ generation both tall and dwarf pea plants appeared. State the ratio obtained. What happened to the characteristic of dwarfness in F₁ plants?

What is speciation? List four factors that could lead to speciation. Which factor does not lead to formation of a new species?

How did Lamarck's theory of evolution differ from Darwin's theory of natural selection? Explain with an example.

In pea plants, round seed (R) is dominant over wrinkled seed (r). A plant with round seeds is crossed with a plant with wrinkled seeds. The F₁ plants all had round seeds. When F₁ plants were selfed, find the phenotypic ratio of the F₂ generation. Show this with the help of a Punnett square.

Explain how acquired traits are different from inherited traits. Why are acquired traits not passed on to the next generation? Give one example each.

Define power of a lens. An object is placed at a distance of 30 cm from a convex lens of focal length 15 cm. List four characteristics of the image formed by the lens.

A concave mirror has a focal length of 15 cm. At what distance should an object be placed in front of the mirror so that it forms an image at 60 cm in front of the mirror? Find the magnification produced by this mirror.

State the laws of refraction of light. A ray of light travels from glass to air. Draw a diagram to show the refraction of light and the angle of refraction.

A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. Find the position, nature, and size of the image formed. Also draw the ray diagram.

What is the difference between a real and a virtual image? Under what conditions does a concave mirror form a virtual image?

The refractive index of glass with respect to air is 3/2. What is the refractive index of air with respect to glass? If the speed of light in vacuum is 3 × 10⁸ m/s, find the speed of light in glass.

List the sign conventions for reflection of light by spherical mirrors. Draw a diagram and apply these conventions for a concave mirror of focal length 15 cm. An object is placed at 40 cm in front of this mirror. Find the image distance using the mirror formula.

Name the type of mirror used in the following and state the reason: (i) Rear-view mirror in vehicles (ii) Solar furnace (iii) Torch light

An object of height 5 cm is placed perpendicular to the principal axis of a concave lens of focal length 10 cm. Use lens formula to determine the position, size, and nature of the image if the distance of the object from the lens is 20 cm.

Draw ray diagrams to show the image formed by a concave mirror when the object is placed: (i) at centre of curvature (ii) between focus and pole.

A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

One half of a convex lens is covered with black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.

What is meant by power of accommodation of the eye? A person cannot see objects clearly at a distance of more than 40 cm. Identify the defect of vision. Give reason. What type of lens should be used to correct this defect?

Draw a diagram of the human eye. Label the cornea, iris, pupil, lens, and retina. What is the function of the iris?

What is dispersion of light? Draw a diagram to show the dispersion of white light through a glass prism. Name the colours in the spectrum of white light in order.

Why does the sky appear blue on a clear day? What colour would the sky appear to an astronaut in outer space? Give reason.

Why does the Sun appear red at sunrise and sunset? Explain the phenomenon responsible for this.

Differentiate between myopia and hypermetropia. Draw ray diagrams to show the image formed in each case and explain the corrective measure.

What is the Tyndall effect? Under what conditions is it observed? Give one example from everyday life.

A person needs a lens of power −5.5 D to correct his distance vision. For correcting his near vision he needs a lens of power +1.5 D. What is the focal length of the lens required for (a) distance vision? (b) near vision? What defects are present?

What is meant by the near point and far point of the human eye? State their values for a normal human eye.

Explain why: (a) Danger signals are made in red colour. (b) Stars appear to twinkle on a clear night. (c) Planets do not twinkle.

State Ohm's law. Draw the V–I graph for a nichrome wire. What does the slope of this graph represent?

Three resistors of 5 Ω, 10 Ω and 15 Ω are connected in series with a 12 V battery. Calculate: (i) the equivalent resistance (ii) the current through the circuit (iii) the voltage across the 10 Ω resistor.

Why is parallel connection preferred over series connection for household wiring? Give two reasons.

An electric lamp of 100 Ω and a toaster of 50 Ω resistance are connected in parallel to a supply of 220 V. Calculate the current drawn from the supply and the total power consumed.

What is resistivity? State its SI unit. How does the resistance of a conductor change when its (i) length is doubled (ii) cross-sectional area is halved?

What is electric power? State its SI unit. A 60 W bulb is connected to a 220 V supply. Find the resistance of the bulb and the current flowing through it.

Two resistors of resistance R₁ = 6 Ω and R₂ = 12 Ω are connected in parallel to a battery of emf 4 V and negligible internal resistance. Draw the circuit diagram. Calculate: (i) Current through each resistor (ii) Total current from the battery.

Why does the tungsten filament of an electric bulb not melt when current flows through it? State two properties of tungsten that make it suitable for this purpose.

What is meant by 1 kWh of electrical energy? Calculate the cost of running a 1500 W geyser for 2 hours per day for 30 days if the cost of electricity is ₹3 per kWh.

State the factors on which the heat produced in a current-carrying conductor depends. Write the expression for it. This is known as which law?

An electric heater draws a current of 5 A from a 220 V supply. What is the cost of using the heater for 3 hours every day for 20 days if the cost of electricity is ₹4.50 per kWh?

Define electric current. What is the direction of conventional current? How is it related to the flow of electrons?

What is the role of fuse in domestic electric circuits? State the characteristic property of the material used for making a fuse wire.

State Fleming's left-hand rule. An electron is moving from East to West in the presence of a magnetic field directed vertically downward. In which direction will the force on the electron act?

What is electromagnetic induction? State the rule used to find the direction of induced current. Name the scientist who discovered this phenomenon.

Draw the pattern of magnetic field lines produced around a straight current-carrying conductor. State the rule used to determine the direction of these field lines.

What is a solenoid? Draw the magnetic field lines around a current-carrying solenoid. Which end of the solenoid acts as the north pole and which as the south pole?

How does the force on a current-carrying conductor in a magnetic field change when: (i) current is doubled (ii) the magnetic field is reversed (iii) the conductor is placed parallel to the field?

Explain the principle and working of an electric generator. Draw a labelled diagram of an AC generator. State one way in which it differs from a DC generator.

What is a galvanometer? How can it be converted into: (i) an ammeter (ii) a voltmeter?

What is the difference between direct current (DC) and alternating current (AC)? Give the frequency of AC used in India. Name one source of each.

Explain the principle and working of an electric motor with the help of a labelled diagram.

State the properties of magnetic field lines. Draw and label the field lines around a bar magnet.

What is the role of earth wire in domestic circuits? Why is it important to connect high-power electrical appliances to earthing?

What happens when a current-carrying conductor is placed in a magnetic field? On what factors does the magnitude of force on the conductor depend?

What is a food chain? Give an example of a food chain from a pond ecosystem. How many trophic levels can a food chain have?

What are biodegradable and non-biodegradable wastes? Give two examples of each. How does accumulation of non-biodegradable substances affect the environment?

What is the 10% law of energy flow? If 10,000 J of energy is available at the producer level, how much energy will be available at the (i) herbivore level (ii) carnivore level?

What is biological magnification? How does it affect organisms at higher trophic levels? Give one example.

Why are the lengths of food chains generally limited to three or four trophic levels?

What is ozone? How is it formed in the upper atmosphere? Why is the depletion of the ozone layer a cause of concern?

What are decomposers? What role do they play in the ecosystem? Name two decomposers.

Distinguish between a food chain and a food web. Draw a simple food web involving four organisms from a grassland ecosystem.

What is the greenhouse effect? Name the gases responsible for it. State two effects of global warming on the environment.

What measures would you suggest to minimise environmental pollution? State any four measures. Why is improper disposal of waste a major environmental problem?

List the components of an ecosystem. Draw a diagram of a simple terrestrial food chain. What will happen if all decomposers are removed from the ecosystem?

What are the disadvantages of using fossil fuels? State two ways by which their excessive use can be reduced.

What is a good source of energy? On what basis would you classify energy sources as (i) renewable (ii) non-renewable?

What is a solar cell? State two advantages and two limitations of using solar cells.

What is nuclear fission? Write the equation for the nuclear fission of U-235. State one advantage and one disadvantage of nuclear energy.

Explain the principle of working of a biogas plant. Draw a labelled diagram. Why is biogas considered a better fuel than wood?

What is the energy transformation that takes place in a hydroelectric power plant? State two disadvantages of constructing large dams.

What is wind energy? State two advantages and two limitations of wind energy. In which states of India are large-scale wind energy farms located?

What is geothermal energy? State any two advantages of using geothermal energy as a source of electricity.

Why is there a need to harness non-conventional sources of energy? Give two examples of non-conventional sources and state one advantage of each.

What is ocean thermal energy? How is it used to generate electricity? What is the minimum temperature difference required for this?

Compare the energy released during the nuclear fission of uranium with the combustion of coal. Why are nuclear power plants not more widespread despite producing large amounts of energy?