CBSE Class 10 Science (086) sample paper 2026–27, with marking scheme

A student counts 12 pulse beats in 10 seconds. The heart rate is:

1. 82 beats per minute
2. 72 beats per minute
3. 12 beats per minute
4. 120 beats per minute

Which of these has the job to carry water and minerals from the roots to the leaves?

1. The anal sphincter
2. Bile
3. The xylem
4. Haemoglobin

A nerve impulse travels 1.2 m along a neuron at 25 m/s. The time taken is:

1. 30 ms
2. 480 ms
3. 48 ms
4. 4.8 ms

In the human body, which of these carries the egg from the ovary; fertilisation takes place here?

1. The vagina
2. The ovaries
3. The oviduct (fallopian tube)
4. The scrotum

Potato usually reproduces asexually by:

1. binary fission
2. fragmentation
3. vegetative propagation
4. spore formation

A pure-breeding plant with axial flowers is crossed with a pure-breeding plant with terminal flowers, and the F₁ plants are self-pollinated. Out of 232 F₂ plants, about how many have terminal flowers?

1. 116
2. 232
3. 174
4. 58

The flow of energy in an ecosystem is:

1. circular
2. in one direction only (unidirectional)
3. random
4. in both directions

Assertion (A): If the kidneys filter 170 litres of fluid in a day and 2 litres leave as urine, about 98.82% of the filtrate is reabsorbed. Reason (R): Most of the filtrate, including water, glucose and salts, is reabsorbed in the kidney tubules.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true, but R is false.
4. A is false, but R is true.

Assertion (A): In the food chain grass → deer → lion, if the producers hold 10,000 J, the lion gets about 100 J. Reason (R): Decomposers break down the dead remains of plants and animals.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true, but R is false.
4. A is false, but R is true.

A strip of black paper is fixed across a leaf of a destarched hibiscus plant, which is then kept in sunlight for 5 hours. The leaf is tested with iodine. (a) What will the iodine test show? (b) What does this show about photosynthesis?

Distinguish between abscisic acid and auxin on the basis of (i) the effect on growth and (ii) an effect that can be seen.

OR

Distinguish between transpiration and translocation on the basis of (i) what moves and (ii) where it happens.

Distinguish between regeneration and fragmentation on the basis of (i) the cells involved and (ii) an example.

A red blood cell travels from the left atrium to the right atrium by the shortest route. (a) Name, in order, the chambers of the heart, blood vessels and organs it passes through. (b) Which of the chambers and vessels on this route (including where it starts and ends) carry oxygenated blood, and which carry deoxygenated blood? (c) Why is it useful that the right and left sides of the heart are kept separate?

In the food chain plants → caterpillar → lizard → snake → hawk: The producers (the plants) hold 1,000 kJ of energy. (a) Using the 10 per cent law, find the energy available to each consumer in the chain. (b) What percentage of the energy held by the plants reaches the hawk? (c) Why is the flow of energy in a food chain said to be unidirectional?

OR

Answer these questions about the ozone layer. (a) Name one harmful effect on human beings of more ultraviolet radiation reaching the Earth. (b) When did the amount of ozone in the atmosphere begin to drop sharply? (c) What step did countries take in 1987 to protect the ozone layer?

A pea-plant experiment

For a school project, Rahul grows two pure-breeding lines of pea plants: plants with round seeds and plants with wrinkled seeds. Rahul dusts pollen from the plants with round seeds onto the stigmas of the plants with wrinkled seeds and raises 43 F₁ plants from the seeds. The F₁ plants are left to self-pollinate, and Rahul raises 532 F₂ offspring from them. In pea plants, R = round, r = wrinkled.

1. What are the genotype and the phenotype of the F₁ plants?

   1 mark

2. About how many of the 532 F₂ offspring are expected to be wrinkled?

   1 mark

3. Give the genotypes of the F₂ offspring with their ratio, and the expected number of each.

   2 marks

   OR

   How many of the round F₂ offspring are expected to be pure-breeding (RR)? Why can Rahul not pick them out just by looking at them?

(a) Name the method of asexual reproduction in each of these organisms and describe how it takes place: (i) Spirogyra, (ii) yeast, (iii) Leishmania. (b) Why do the offspring of asexual reproduction look almost exactly like the parent, and why is a little variation still seen?

OR

The body cells of a frog have 26 chromosomes. (a) How many chromosomes are there in (i) each of its gametes (a sperm and an egg) and (ii) the zygote formed at fertilisation? (b) Gametes are made by a special division that halves the chromosome number. If they were made by ordinary division instead, how many chromosomes would a body cell have after 4 generations? (c) Why is the copying of DNA essential in reproduction, and why are the copies not always exactly alike? (d) Which kind of reproduction, sexual or asexual, produces more variation, and why?

The reaction Zn + H₂SO₄ → ZnSO₄ + H₂ is an example of:

1. a combination reaction
2. a double displacement reaction
3. a displacement reaction
4. a decomposition reaction

Solutions of barium chloride (BaCl₂) and dilute sulphuric acid (H₂SO₄) are mixed. The precipitate formed is:

1. H₂SO₄
2. NaCl
3. BaCl₂
4. BaSO₄

What colour is red litmus in sodium hydroxide solution?

1. pink
2. green
3. red
4. blue

Solutions P, Q, R and S have pH values of 1, 2, 10, 12 respectively. Which is the most acidic?

1. S
2. Q
3. P
4. R

The oxide Fe₂O₃ is:

1. basic
2. amphoteric
3. neutral
4. acidic

Which of these will decolourise bromine water?

1. C₂H₄
2. C₂H₅COOH
3. C₃H₇OH
4. C₄H₉Cl

Soaps do not work well in hard water because they:

1. become acidic
2. form an insoluble scum with calcium and magnesium ions
3. dissolve too quickly
4. evaporate

Assertion (A): A solution with a pH of 10 is basic. Reason (R): A pH below 7 means a solution is acidic, and a pH above 7 means it is basic.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true, but R is false.
4. A is false, but R is true.

Rohan notices a reddish-brown, flaky coating on the chain of a bicycle at home. (a) Name this process and the substance formed, and state the two conditions needed for it. (b) Suggest a way to prevent it for the chain of a bicycle, and explain how the method works.

Dev adds dilute nitric acid to magnesium carbonate powder in a test tube and passes the gas given off through lime water. (a) Write the balanced chemical equation for the reaction in the test tube and name the salt formed. (b) Name the gas, state what happens to the lime water, and write the equation for this change. (c) Write a general word equation for the reaction of an acid with a metal carbonate or hydrogencarbonate.

OR

Iron(III) chloride (FeCl₃) is to be made by a neutralisation reaction. (a) Name the acid and the base it is formed from, and say whether each is strong or weak. (b) Write the balanced chemical equation for its formation. (c) Will a solution of iron(III) chloride in water have a pH less than 7, equal to 7 or more than 7? Give a reason.

A zinc strip is placed in copper sulphate solution (CuSO₄) and left for some time. (a) Will a reaction take place? Give a reason. (b) Write the balanced chemical equation for the reaction. (c) Name a metal that could not displace copper from this solution, and give a reason.

A burning feeling after dinner

After a heavy, spicy dinner at a wedding, Vikram complains of a burning feeling in the chest and pain in the stomach. The doctor explains that the stomach makes a dilute acid, with a pH of about 3, which helps to digest food, and that too much of it causes indigestion and pain. The doctor suggests a spoon of baking soda in water (NaHCO₃), a mild base that is called an antacid.

1. Name the acid made by the stomach.

   1 mark

2. Why is a mild base, and not a strong base such as sodium hydroxide, given as an antacid?

   1 mark

3. Write the balanced chemical equation for the reaction of the antacid with the stomach acid, and name this type of reaction.

   2 marks

   OR

   Before the antacid, the stomach juice had a pH of about 3. Will the pH rise or fall after the antacid acts? Explain in terms of hydrogen ions.

Two hydrocarbons are P (C₃H₈) and Q (C₃H₆). (a) Which of them is saturated and which is unsaturated? Give a reason. (b) Q reacts with hydrogen in the presence of a nickel catalyst. Write the balanced equation and give one industrial use of this kind of reaction. (c) P reacts with chlorine in sunlight. Write the balanced equation for the first step and name the type of reaction. (d) Write the balanced equation for the complete combustion of P. (e) How could you tell P and Q apart using bromine water?

OR

Butanoic acid (C₃H₇COOH) is warmed with ethanol (C₂H₅OH) and a few drops of concentrated sulphuric acid. (a) Write the balanced chemical equation and name the organic product. (b) What is the role of the concentrated sulphuric acid, and how could you tell that the product has formed? (c) The product is heated with sodium hydroxide solution. Write the balanced equation for this reaction. (d) Write the balanced equation for the reaction of butanoic acid with sodium hydrogencarbonate. (e) Name the gas given off in (d) and give a test for it.

The radius of curvature of a concave mirror is 12 cm. Its focal length is:

1. −6 cm
2. −12 cm
3. −7 cm
4. 6 cm

A charge of 225 C flows through a wire in 50 s. The current is:

1. 11,250 A
2. 5.5 A
3. 4.5 A
4. 0.22 A

Assertion (A): A current flowing towards the north in a magnetic field pointing east feels a force vertically downwards. Reason (R): Magnetic field lines are closed curves.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true, but R is false.
4. A is false, but R is true.

Meera passes white light through a glass prism and looks at the indigo and red parts of the spectrum on a screen. Which of the two is bent more by the prism? Give a reason.

Resistors of 19 Ω and 20 Ω are connected in series to a 78 V battery. Find the current in the circuit and the potential difference across the 19 Ω resistor.

OR

A solenoid of 250 turns has ends L and M. Seen from end L, the current flows clockwise. (i) Which end behaves as a north pole? (ii) The current is now reversed. Does the north pole of a compass placed near end M point towards or away from end M?

Three resistors of 12 Ω, 16 Ω and 48 Ω are connected in parallel across a battery of 144 V. Find (i) the equivalent resistance, (ii) the current through each resistor, and (iii) the total current drawn from the supply.

A solenoid of 750 turns has ends A and B. When it is connected to a battery, the current, seen from end B, flows anticlockwise round the coil. (i) Which end of the solenoid behaves as a north pole? (ii) The north pole of a bar magnet is brought near end A. Is it attracted or repelled? (iii) Describe the magnetic field inside the solenoid, and give one way to make it stronger.

Three resistors of 18 Ω, 27 Ω and 54 Ω are connected in parallel across a DC supply of 216 V. Find (i) the equivalent resistance, (ii) the current through each resistor, and (iii) the total current drawn from the supply.

Colours in the sky

During a weekend outing, Rohan watches the sun set from a beach. The sky overhead is blue, but the sun near the horizon looks reddish. On the way back, Rohan notices that the warning lamps at a road repair site are red. At home, Rohan passes a narrow beam of white light through a glass prism and sees a band of colours on a white wall.

1. Of these colours, which is scattered the most by very fine particles in the air?

   1. yellow
   2. blue
   3. violet
   4. indigo
   1 mark

2. Why are signal and warning lights made red?

   1 mark

3. Why does the clear sky look blue from the ground? How would it look to an astronaut far above the atmosphere?

   2 marks

   OR

   Why does the sun look reddish when it is near the horizon?

Light travels at 2.4 × 10⁸ m/s in a gemstone (medium A) and at 1.5 × 10⁸ m/s in a crystal (medium B). The speed of light in vacuum is 3 × 10⁸ m/s. (a) Find the absolute refractive index of A and of B. (b) Find the refractive index of B with respect to A. (c) A ray of light passes obliquely from A into B. Does it bend towards or away from the normal? Give a reason. (d) A third medium C has a refractive index of 1.92 with respect to A. Find the speed of light in C. (Give answers to 2 decimal places where needed.)

OR

A convex lens of focal length 20 cm is used to form a sharp, real image on a screen that is one-half the size of the object. (a) How far from the lens must the object be placed? (b) How far from the lens is the screen, and what is the distance between the object and the screen? (c) Find the power of the lens. (d) Describe the image if the object is then moved to a point between the lens and its principal focus.