CBSE Class 10 Science Important Questions 2027 (Repeated in Board Exams)

C₆H₁₂O₆(aq) + 6O₂(g) -> 6CO₂(g) + 6H₂O(l). The above reaction is an example of - (A) Displacement Reaction (B) Endothermic Reaction (C) Exothermic Reaction (D) Neutralisation Reaction

Identify the type of each of the following reactions stating the reason for your answers. A. Fe₂O₃ + 2Al -> Al₂O₃ + 2Fe + heat B. Pb(NO₃)₂ + 2KI -> PbI₂(down-arrow) + 2KNO₃

Identify 'p', 'q' and 'r' in the following balanced reaction: p Pb(NO₃)₂(s) --Heat--> q PbO(s) + r NO₂(g) + O₂(g) A. 2,2,4 B. 2,4,2 C. 2,4,4 D. 4,2,2

The volume ratio of hydrogen and oxygen gases liberated during electrolysis of water is (A) 1 : 1 (B) 2 : 1 (C) 4 : 1 (D) 1 : 2

Select from the following a decomposition reaction in which source of energy for decomposition is light: (a) 2FeSO₄ -> Fe₂O₃ + SO₂ + SO₃ (b) 2H₂O -> 2H₂ + O₂ (c) 2AgBr -> 2Ag + Br₂ (d) CaCO₃ -> CaO + CO₂

MnO₂ + 4HCl -> MnCl₂ + 2H₂O + Cl₂. The reaction given above is a redox reaction because in this case: (a) MnO₂ is oxidised and HCl is reduced. (b) HCl is oxidised. (c) MnO₂ is reduced. (d) MnO₂ is reduced and HCl is oxidised.

[case context] pH scale predicts strength of acids and bases via hydrogen ion concentration. Three solutions A, B and C showed pH as 3, 5 and 7. Which solution has the highest concentration of H^+ ions?

An aqueous solution turns red litmus blue. Excess addition of which of the following solution would reverse the change? (A) Sodium hydroxide (B) Hydrochloric acid (C) Baking soda (D) Slaked lime

[Case: Seawater contains many dissolved salts; common salt is separated from these, deposits of solid rock salt (brown due to impurities) are mined like coal, and common salt is an important raw material for chemicals of daily use.] Write balanced chemical equations to show the products formed during electrolysis of brine.

When excess of carbon dioxide is passed through lime water, the milkiness disappears because A. water soluble calcium carbonate converts to water soluble calcium bicarbonate. B. insoluble calcium carbonate converts to water soluble calcium bicarbonate. C. water soluble calcium carbonate converts to insoluble calcium bicarbonate. D. insoluble calcium carbonate converts to insoluble calcium bicarbonate.

(a) A compound 'A' is used in soda-lime fire-extinguisher and decomposes on heating to form compound 'B'. Compound 'B' is used for removing permanent hardness of water. Identify 'A' and 'B'. (b) Write chemical formula of Plaster of Paris. At what temperature gypsum is heated to obtain Plaster of Paris?

(i) The pH of a sample of tomato juice is 4.6. How is this juice likely to be in taste? Give reason to justify your answer. (ii) How do we differentiate between a strong acid and a weak base in terms of ion-formation in aqueous solutions? (iii) The acid rain can make the survival of aquatic animals difficult. How?

(i) Which method will be used to convert each of them to their respective metal oxides? (a) Carbonate ore (b) Sulphide ore. (ii) Write a chemical reaction to illustrate the use of aluminium for joining cracked railway tracks. (iii) During extraction of metals, electrolytic refining is used to obtain pure metals. Which material will be used as anode and cathode for the refining of copper metal by this process?

Four statements about the reactions of oxides with dilute hydrochloric acid and aqueous sodium hydroxide are listed. I. Aluminium oxide reacts with both dilute hydrochloric acid and aqueous sodium hydroxide. II. Calcium oxide reacts with dilute hydrochloric acid and aqueous sodium hydroxide. III. Zinc oxide reacts with both dilute hydrochloric acid and aqueous sodium hydroxide. IV. Sulphur dioxide does not react with either dilute hydrochloric acid or aqueous sodium hydroxide. Which statements are correct? A. I and II B. I and III C. II and IV D. III and IV

An iron nail is added to each of the two test tubes 'P' and 'Q' containing aqueous copper (II) sulphate, and aqueous silver nitrate respectively. Which of the following observation is correct? A. In test tube 'P' iron nail is coated with a blue coating and in test tube 'Q' there is no reaction. B. Iron nail is coated with a brown coating in test tube 'P' and silver coating in test tube 'Q'. C. There is no reaction in either of the test tubes 'P' or 'Q'. D. There is no reaction in test tube 'P' but a silver coating on iron nail is seen in test tube 'Q'.

An element 'X' is stored in kerosene, and cannot be extracted from its ore using a reducing agent. 'X' forms an ionic compound on reaction with chlorine. (i) Can we store 'X' in water? Give reason to support your answer. (ii) Identify element 'X'. Name the process used and write the equation for extraction of 'X' from its ore.

The electronic structures of atoms P and Q are shown in the given figure. Based on the information given above, answer the following questions: (a) If P and Q combine to form a compound, what type of bond is formed between them? (b) Give the chemical formula of the compound formed. (c) The compound so formed is dissolved in water. Is the resultant solution acidic or basic in nature? Justify your answer. (d) Write the chemical equation for the reaction between 'Q' and ethanol. (e) What will be the formula of the compound formed when 'P' undergoes bonding with carbon?

Which one of the following metals does not react with cold water? (A) Sodium (B) Potassium (C) Calcium (D) Magnesium

The products formed when Aluminium and Magnesium are burnt in the presence of air respectively are : (A) Al₃O₄ and MgO₂ (B) Al₂O₃ and MgO (C) Al₃O₄ and MgO (D) Al₂O₃ and MgO₂

(i) A carbon compound X is a good solvent. On reaction with sodium, X forms two products Y and Z. Z is used to convert vegetable oil into vegetable ghee. Identify and name X, Y and Z. Also write the equation of reaction of X with sodium to justify your answer. (ii) Write chemical equation to show what happens when ethanol: (I) burns in oxygen/air. (II) is heated at 443 K in excess conc. H₂SO₄. (III) reacts with acidified potassium dichromate.

Attempt either option A or B. B. (i) 'A' & 'B' are sodium salts of long-chain carboxylic acid and long chain Sulphonic acid respectively. Which one of A or B will you prefer as a cleansing agent while using underground water (hand pump water)? Give the reason for your answer. (ii) Elaborate on the process of cleansing action. Illustrate micelle with the help of labelled diagram. (iii) Write the chemical equation of the preparation of soap from an ester CH₃COOCH₃. What is the name of this process?

(i) How would you name the following: I. CH_3-CH_2-C(=O)H (i.e. CH_3-CH_2-CHO); II. CH_3-C≡CH. (ii) When ethanol reacts with ethanoic acid in the presence of conc. H₂SO₄, a substance with sweet smell is produced. Answer the following: I. State the class of compounds to which the sweet smelling compounds belong. II. Write the chemical equation for the reaction. (iii) Why soaps do not produce foam with hard water?

(i) Carbon cannot form C⁴⁺ cation and C^4- anion. Explain. (ii) Define homologous series of carbon compounds. Why are the melting and boiling points of C₄H₁₀ higher than C₃H₈ or C₂H₆? (iii) What happens when ethanol is heated with acidified potassium dichromate?

Carbon compounds: (i) are good conductors of electricity. (ii) are bad conductors of electricity. (iii) have strong forces of attraction between their molecules. (iv) have weak forces of attraction between their molecules. The correct statements are: (a) (i) and (ii) (b) (ii) and (iii) (c) (ii) and (iv) (d) (i) and (iii)

Which of the following options indicates the products formed after breakdown of the glucose in our muscle cells when there is lack of oxygen? A. Ethanol + carbon dioxide + Energy B. Lactic acid + Energy C. Lactic acid + carbon monoxide + Energy D. Carbon dioxide + Water + Energy

Explain the mechanism by which the water is transported in plants.

[Case: Maintenance functions require energy from food prepared by autotrophs.] State in proper sequence the events that occur in synthesis of food by desert plants.

In human beings the oxygen rich blood is pumped out to the body by: (A) contraction of right atrium (B) relaxation of left ventricle (C) contraction of right ventricle (D) contraction of left ventricle

Attempt either option A or B. B. Explain the role of the following enzymes in the process of digestion of food in humans: (i) Salivary amylase (ii) Pepsin (iii) Trypsin (iv) Lipase

(a) Draw a labelled diagram showing open and closed stomatal pore. (b) List the main events that occur during the process of photo-synthesis. (c) Write a balanced chemical equation showing photo-synthesis in plants.

Observe the given figure and select the statement that correctly states how these fungi obtain nutrition. (A) By eating the bread on which it is growing. (B) By using nutrients from the bread to prepare their own food. (C) By breaking down the nutrients of bread outside the body and then absorbing them. (D) By allowing other organisms to grow on the bread and then consuming them.

(a) Draw a well-labelled diagram of nephron and label atleast 4 of its parts. (b) Write the role of capillary cluster inside Bowman's capsule. (c) What is meant by selective reabsorption?

Besides minimising the loss of blood, why is it essential to plug any leak in a blood vessel ? Name the component of blood which helps in this process and state how this component performs this function.

Following are the statements about the different parts of the brain. Select the correct statements. (i) The thinking part of the brain is the forebrain. (ii) Centres for smell, hearing, memory, sight are located in forebrain. (iii) Salivation, vomiting, blood pressure are controlled by medulla in the hind brain. (iv) Cerebellum does not control the posture and balance of the body. (A) (i), (ii) and (iii) (B) (ii), (iii) and (iv) (C) (i), (ii) and (iv) (D) (i), (iii) and (iv)

[case context] Plants show movements in response to environmental stimuli regulated by plant hormones. What role does auxin play in the growth of plants?

[case context] Plants show movements in response to environmental stimuli regulated by plant hormones. Differentiate between movement shown by the sensitive plant and tropic movement by plants (Two points).

Draw and explain how the nerve cells help in transmission of impulses?

The blood glucose level in a patient was very high. It may be due to inadequate secretion of: A. growth hormone from pituitary gland B. oestrogen from ovary C. insulin from pituitary gland D. insulin from pancreas

Sunil unconsciously touched the hot iron rod and immediately withdrew his hand. Which type of action is involved? Also define this action. Draw a flow chart to show the path followed for this action.

Puneet wanted to grow banana plants. (i) Based on your knowledge on plant reproduction should he opt for seeds or any alternate method of reproduction? Justify your answer. (ii) Offsprings of a banana plant usually show very little variation. What causes variation and are variations good or bad? Justify.

Draw labelled diagrams to show different stages of budding in Hydra.

(i) Differentiate between self-pollination and cross-pollination. (ii) Identify A, B and C in the diagram given below (a diagram of a flower/pistil showing pollen germination and the ovule - see figure) and write one function of each.

(i) Write the functions of the following parts of human female reproductive system: (I) Ovary (II) Fallopian tube (III) Uterus. (ii) State briefly two contraceptive methods used by human males.

In which of the following organisms, multiple fission is a means of asexual reproduction? (a) Yeast (b) Leishmania (c) Paramoecium (d) Plasmodium

Two pea plants, one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds were crossed with each other which produced F₁ progeny that have only round yellow (RrYy) seeds. When F₁ plants are self-pollinated, the F₂ progeny will have which new combination of characters, as compared to the parents: (i) Round, yellow (ii) Round, green (iii) Wrinkled, yellow (iv) Wrinkled, green. Correct options are: (A) (i) and (ii) (B) (i) and (iv) (C) (ii) and (iv) (D) (i) and (iii)

Study the given table and answer the following questions: [Parents: A pea plant with red flowers was crossed with a pea plant with white flowers. | F₁: 30 seeds were sown and all bore plants with red flowers. | F₂: 44 seeds were sown, 33 plants bore red flowers and 11 plants bore white flowers.] (a) Depict the information given in the table in the form of a cross. (b) Deduce the F₂ phenotypic ratio / F₂ ratio showing external look as well as genotypic/genetic makeup, ratio.

In snails individuals can begin life as male and depending on environmental conditions they can become female as they grow. This is because A. male snails have dominant genetic makeup. B. female snails have dominant genetic makeup. C. expression of sex chromosomes can change in a snail's life time. D. sex is not genetically determined in snails.

Chromosomes: (i) carry hereditary information from parents to the next generation. (ii) are thread like structures located inside the nucleus of an animal cell. (iii) always exist in pairs in human reproductive cells. (iv) are involved in the process of cell division. The correct statements are: (a) (i) and (ii) (b) (iii) and (iv) (c) (i), (ii) and (iv) (d) (i) and (iv)

[case context: Mendel's experiments on inheritance in garden pea.] Write one difference between dominant and recessive trait.

Consider the following statements: (i) The sex of a child is determined by what it inherits from the mother. (ii) The sex of a child is determined by what it inherits from the father. (iii) The probability of having a male child is more than that of a female child. (iv) The sex of a child is determined at the time of fertilisation when male and female gametes fuse to form a zygote. The correct statements are: (a) (i) and (iii) (b) (ii) and (iv) (c) (iii) and (iv) (d) (i), (iii) and (iv)

The given figure shows the formation of an image with an optical instrument (shown schematically as a rectangle); an upright object forms an image with the distances 10 cm and 20 cm marked. A. Identify the optical instrument (shown schematically as a rectangle) in the image. B. What type of image is formed in this case? C. Based on the measurements given in the image, calculate the focal length of the instrument. (For visually impaired students: A. Under what conditions can a convex lens form a virtual image? B. Why does a piece of paper catch fire if we allow sunlight to pass through a convex lens onto the paper?)

Arnav was making notes and he wrote down the following statements from his understanding of reflection from curved surfaces. I. Concave mirrors can produce both real and virtual images depending on the position of the object. II. Convex mirrors always produce real, inverted images regardless of the object's position. III. In both concave and convex mirrors, the image location can be determined using the mirror formula 1/f = 1/v + 1/u where f is the focal length, v is the image distance, and u is the object distance. Choose from the following the correct option that lists the correct statements about reflection from curved surfaces. A. I and II B. I, II and III C. II and III D. I and III

[case context] A reflecting telescope uses curved mirrors and a plane mirror to form an image at the eye-piece. Explain with the reason, what kind of optical device (type of lens or mirror) is used at the eye-piece.

[case context] A ray diagram shows image formation by a reflecting telescope, which uses large precisely-shaped curved mirrors (and a plane mirror) to gather and focus incoming light to a focal point where the image is formed for observation at the eye-piece. What kind of image of a star is seen by the observer in the eye-piece?

[case context] A ray diagram shows image formation by a reflecting telescope that uses large curved mirrors to gather and focus light. What kind of mirror is used in this reflecting telescope?

[case context] A reflecting telescope uses curved mirrors and a plane mirror to form an image. OR alternative for (c): What is the role of plane mirror in image formation by this telescope?

Draw ray diagrams to show the nature, position and relative size of the image formed by a convex mirror when the object is placed (i) at infinity and (ii) between infinity and pole P of the mirror.

An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position of the image formed by the mirror.

The given figure shows a corrective measure for a particular defect of vision. (i) Identify the defect of vision and state what kind of lens is used to correct this deficiency. (ii) Draw and label a ray diagram that shows the defect of vision in the above case before correction. (For visually impaired students: (i) What is dispersion of light? (ii) Explain the condition under which dispersion happens? (iii) Give one reason that causes presbyopia.)

Choose the correct option from the below which explains the reason for us to perceive the day sky as blue. A. As sunlight passes through the atmosphere, shorter wavelengths, such as blue are scattered more than other colors. B. The sky appears blue because all colors are scattered equally, but blue light is stronger and more visible to the human eye. C. The blue color of the sky is due to longer wavelengths like red and orange scattering more than shorter wavelengths, making blue stand out more. D. The atmosphere contains blue-colored particles that give the sky its blue appearance.

White light is incident on a glass prism; ray x enters and two emergent rays A (upper) and B (lower) leave the prism. Choose the correct option for the colour of rays for A and B. A. Ray A Blue, Ray B Red B. Ray A Green, Ray B Yellow C. Ray A Red, Ray B Violet D. Ray A Violet, Ray B Indigo

The vision defect which arises due to gradual weakening of the ciliary muscles and diminishing flexibility of eye lens is: (A) Myopia (B) Hypermetropia (C) Presbyopia (D) Myopia and hypermetropia both

The pair of eye parts responsible for admitting different amount of light in to the eyes is (A) Iris and pupil (B) Ciliary muscles and pupil (C) Retina and Iris (D) Ciliary muscles and cornea

Explain the phenomenon of rainbow formation in the sky. Draw the labelled ray diagram in support of your explanation.

(i) The given electric circuit is a part of an electrical device. Use the information given in the electric circuit diagram to calculate: (I) Potential difference across the ends of resistor R₂. (II) Value of resistor R₂. (III) Value of resistor R₁. [Circuit data: 12 V source with key K; branch with R₁; a 4.0 Ohm resistor carrying 1.5 A; resistor R₂ in parallel; a 2.0 Ohm resistor; total line current 2.0 A.] (ii) Write the factors on which resistance of a conductor depends and derive the formula for resistance of a given conductor.

(i) How much electric current will an electric iron draw from 220 V source if the resistance of its heating element when hot, is 55 Ohm? Calculate the power consumed by the electric iron when it is operated at 220 V. (ii) In a house, 3 bulbs of 100 watt each, are lit for 5 hours daily and an electric heater of 1.0 kW is used for half an hour daily. Calculate the total energy consumed in a month of 30 days and its cost at the rate of Rs. 3.60 per kWh. (iii) With reason explain, why are alloys commonly used to make elements of electrical heating devices.

Find out the following in the electric circuit given in the figure (an 8 V cell in series with a 4 ohm resistor and ammeter A₁, connected to two 8 ohm resistors joined in parallel between points C and D, with ammeter A₂ in the return path): (i) Effective resistance of two 8 ohm resistors in the combination. (ii) Current flowing through the 4-ohm resistor.

(a) Write the relationship between resistivity and resistance of a cylindrical conductor of length l and area of cross-section A. Hence derive the SI unit of resistivity. (b) Why are alloys used in electrical heating devices ?

Attempt either option A or B. B. The given figure shows two resistors X (R) and Y (2R) connected in series to a battery. The power dissipated for this combination is P₁. When these resistors are connected in parallel to the same battery then the power dissipated is given by P₂. Find out the ratio P₁/P₂.

A fuse in electric circuit is rated 4 A. Can it be used with an electric heater of rating 2 kW, 200 V? Explain your answer.

Attempt either option A or B. A. The electric circuit (given figure) in a clothes dryer contains two heaters X and Y in parallel connected to a 230 V power supply. When both switches are closed, the current in X is 3.5 A. Analyse the circuit and answer: (i) Calculate the power developed in heater X. (ii) If the resistance of X is double that of Y calculate the current in heater Y.

A wire of resistance R is cut into three equal parts. If these three parts are then joined in parallel, calculate the total resistance of the combination so formed.

In the given circuit calculate the power consumed in watts in the resistor of 2 ohm: [circuit diagram shows a 1 ohm resistor and a 2 ohm resistor in series with a 6 V battery]

On the basis of the given circuit arrangement, answer the following questions: (a) What happens to the rod AB when the key K is closed and why? (b) Name and state the rule that determines this behaviour of the rod AB in the above situation.

Magnetic field lines are shown in the given diagram (field lines around a current loop with points X and Y marked, near a magnet labelled N-S). A student makes a statement that the magnetic field at X is stronger than at Y. (i) Explain with reason if the student's claim is correct. (ii) Also redraw the diagram and mark the direction of magnetic field lines.

(i) Draw the pattern of magnetic field lines of (1) a current carrying solenoid (2) a bar magnet. (ii) List two distinguishing features between the two fields.

Assertion (A): No two magnetic field lines are found to cross each other. Reason (R): The compass needle cannot point towards two directions at the point of intersection of two magnetic field lines. Select the correct answer: (A) Both A and R are true and R is the correct explanation of A. (B) Both A and R are true, but R is not the correct explanation of A. (C) A is true, but R is false. (D) A is false, but R is true.

How is an electromagnet made? Write any two ways by which the strength of electromagnet can be increased.

The pattern of the magnetic field produced inside a current carrying solenoid is: [four field-pattern diagrams labelled (a), (b), (c), (d) are given as the options]

Assertion (A): Highest percentage of pesticides is found in tertiary consumers in a food chain. Reason (R): Chemicals / pesticides get accumulated progressively at each trophic level. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

Explain why food chains generally consist of three or four steps.

Given below are some of the statements regarding our environment: (i) Change in our life-styles have resulted in greater amounts of waste material generation. (ii) Changes in attitude have resulted in use of more disposable things. (iii) Changes in packaging has resulted in much of our waste becoming non-biodegradable. (iv) Organic farming. Which amongst these is not leading to any damage of environment? (A) (i), (ii), (iii) (B) (iv) (C) (i) and (iii) (D) (ii) and (iv)

About 100 acres of forest land was declared as Natural reserve park. The following organisms were predominant in the Natural reserve park: rabbit, frog, grass, fish, fox, water insects, zebra, peacock, snake, trees, bird, owl, insects, tiger, vulture, duck. Create a food web comprising two separate food chains with different producers by using the above data.

Assertion (A): If the lions are removed from a food chain it will not affect the food chain, however if the plants are removed from a food chain it will disturb the ecosystem. Reason (R): Plants are producers who can make food using sunlight, while lions are consumers. [Options: A. Both A and R are true, and R is the correct explanation of A. B. Both A and R are true, and R is not the correct explanation of A. C. A is true but R is false. D. A is false but R is true]

Which of the following groups do not constitute a food chain ? (i) Wolf, rabbit, grass, lion (ii) Plankton, man, grasshopper, fish (iii) Hawk, grass, snake, grasshopper, frog (iv) Grass, snake, wolf, tiger (A) (i) and (iv) (B) (i) and (iii) (C) (ii) and (iii) (D) (ii) and (iv)

A gas 'X' which is a deadly poison is found at the higher levels of atmosphere and performs an essential function. Name the gas and write the function performed by this gas in the atmosphere. Which chemical is linked to the decrease in the level of this gas? What measures have been taken by an international organization to check the depletion of the layer containing this gas?

(i) Why does a kitchen garden called an artificial ecosystem while a forest is considered to be a natural ecosystem? (ii) While designing an artificial ecosystem at home, write any two things to be kept in mind to convert it into a self-sustaining system. Give reason to justify your answer.