CBSE Class 10th Science Answer Key 2026 (Unofficial) - Set Wise Question Paper Solution

The CBSE Class 10th Science Board Exam 2026 was successfully conducted today, 25 February 2026, in offline mode across various exam centres affiliated with the Central Board of Secondary Education (CBSE). Students can now check the CBSE Class 10 Science unofficial answer key 2026 here, along with a detailed paper analysis, difficulty level, and section-wise review. The unofficial answer key will be released today around 2:00 PM after the exam

CBSE Class 10 Science Exam 2026 - Key Highlights

• Board: Central Board of Secondary Education (CBSE)
• Class: 10th
• Subject: Science
• Exam Date: 25 February 2026
• Exam Timing: 10:30 AM to 1:30 PM (3 hours)
• Reporting Time: 10:00 AM
• Question Paper Type: Theory (80 marks)
• Internal Assessment: 20 marks
• Mode of Exam: Offline (Pen and Paper)​
• Unofficial Answer Key: Expected at 2:00 PM (today)

CBSE Class 10 Science Answer Key 2026 (Unofficial) – Release Time

The CBSE Class 10 Science paper ended at 1:30 PM and students will be able to access the unofficial answer key for all sets around 2:00 PM. Coaching institutes and subject experts will solve the question paper and provide a set-wise solution PDF and video explanation for students

Students can use this unofficial answer key to:

• Estimate their probable marks before the official CBSE answer key and result.​

• Cross-check objective and short-answer questions.​

• Analyse their performance and plan upcoming board exams accordingly.

Section A: Biology

Section B: Chemistry

Section C: Physics

CBSE Class 10 Science 2026 Answer Key (All Sets)

8. Assertion & Reason
Assertion (A): Blood plasma transports carbon dioxide in dissolved form, while oxygen is transported by respiratory pigments.

Reason (R): Carbon dioxide is more soluble in water than in oxygen.

Answer: Assertion (A) is true, but Reason (R) is false.

Explanation: While the Assertion is scientifically accurate, the Reason is phrased incorrectly. Carbon dioxide is more soluble in water than oxygen is in water; comparing its solubility to "oxygen" itself is a logical error.

9. Assertion & Reason

Assertion (A): There are generally a greater number of individuals at the lower trophic levels of an ecosystem.

Reason (R): The greatest number is of the producers.

Answer: Both (A) and (R) are true and (R) is the correct explanation of (A).

Explanation: In most ecosystems, the pyramid of numbers is upright. Producers (the lowest trophic level) must be the most numerous to provide enough energy to support the fewer consumers above them.

10. Descriptive Questions

(a) Hormonal Regulation
Statement: "The timing and the amount of hormone secreted by a gland are regulated in the human body."
Justification: This is regulated by a feedback mechanism.

Example: When blood glucose levels rise, the pancreas detects this change and secretes insulin to lower the sugar levels. Once the levels fall to a normal range, the secretion of insulin is reduced or switched off.

OR
(b) Limitations of Electrical Impulses
While electrical impulses are fast, they have two primary limitations:

Limited Reach: Electrical impulses reach only those cells that are connected by nervous tissue; they cannot reach every single cell in the body.

Recovery Time: Once an electrical impulse is generated and transmitted, the cell needs time to reset its mechanisms before it can generate a new impulse. This means cells cannot continuously create and transmit impulses.

11. Survival and Variation

Statement: "Variation is useful for the survival of species over time."

Explanation: Environments change constantly (temperature shifts, water level changes, etc.). If a population is identical and the environment changes drastically, the entire species could be wiped out. Variation ensures that some individuals might possess traits that allow them to survive the change.

Example: In a population of bacteria living in temperate waters, most might die if the water temperature increases due to global warming. However, a few heat-resistant variants would survive and regrow the population.

Question 30: Negative Magnification Greater than OneThe correct option is (A) Concave mirror; Nature of image – real.

Reasoning:Sign of Magnification (m): In optics, a negative magnification signifies that the image is real and inverted.Magnitude (|m| > 1): A magnification greater than one means the image is enlarged (magnified).Mirror Type: * A convex mirror always produces virtual, erect, and diminished images (m is always positive and less than 1).A concave mirror can produce a real, inverted, and enlarged image when the object is placed between the center of curvature (C) and the principal focus (F).

Question 31: Spectrum Sequence from Top to BottomThe correct option is (B) Red, Yellow, Green, Blue, Violet.

Reasoning:When white light passes through a glass prism, it splits into its constituent colors (VIBGYOR).Refraction/Bending: Different colors bend by different amounts. Red light has the longest wavelength and bends the least, while Violet light has the shortest wavelength and bends the most.Position on Screen: Because Red bends the least, it appears at the top of the spectrum. Because Violet bends the most, it appears at the bottom.The sequence from top to bottom is Red, Orange, Yellow, Green, Blue, Indigo, and Violet. Option (B) follows this specific descending order correctly.

Question 32

Assertion (A): "Direction of force exerted on a current-carrying conductor placed in a magnetic field remains same if the directions of both magnetic field and current flowing through the conductor are reversed."

Status: True. According to Fleming's Left-Hand Rule, the force depends on both the direction of the magnetic field and the current. If you reverse one, the force reverses. If you reverse both, they cancel each other out, and the direction of the force remains the same.

Reason (R): "The direction of force exerted on a current-carrying conductor placed in an external magnetic field can be determined by using magnetic compass."

Status: False. A magnetic compass is used to detect the presence and direction of a magnetic field, not the mechanical force exerted on a conductor. The correct tool to determine the direction of force is Fleming's Left-Hand Rule.

Final Answer

In standard multiple-choice formats for these types of questions, the correct choice would be: Assertion (A) is true, but Reason (R) is false.

5: Balanced Equation for Photosynthesis

The correct option is (D).

Section - A - Biology

1. In human beings, the implantation of fertilised egg takes place in which part of female reproductive system?

• (C) Uterus

  • Explanation: After fertilization occurs in the oviduct (Fallopian tube), the zygote travels to the uterus, where it attaches to the thickened lining (endometrium). This process is known as implantation.

2. Yeast multiplies by which of the following methods?

• (D) Budding

  • Explanation: Yeast is a unicellular fungus that primarily reproduces asexually through budding, where a small bulb-like projection (bud) forms on the parent cell, matures, and eventually detaches to become a new individual.

3. Answer: (C) Guard cells

Explanation

• Stomata are tiny pores found on the surface of leaves that allow for gas exchange and transpiration. The "opening and closing" mechanism is a biological process regulated by Guard cells:
• Opening: When water flows into the guard cells, they become turgid (swollen) and curve outward, which pulls the stomatal pore open.
• Closing: When the guard cells lose water, they become flaccid (shrunken) and straighten out, which causes the pore to close to prevent water loss.

4: Correct Option: (D)

Explanation:

• Phase 1: Glucose is broken down into Pyruvate in the cytoplasm (Glycolysis).

• Phase 2: When there is a lack of oxygen in muscle cells (often during vigorous exercise), pyruvate is converted into lactic acid rather than entering the mitochondria. This buildup of lactic acid is what causes muscle cramps.

5. Which of the following is a non-biodegradable pollutant?

Answer: (B) DDT

• Reason: Paper, wood, and vegetable peels are organic materials that can be broken down by microorganisms over time. DDT (Dichlorodiphenyltrichloroethane) is a synthetic pesticide that persists in the environment for a very long time without breaking down.

6. When a human egg is fertilized by a sperm having 'Y' chromosome, the zygote has the following combination of chromosomes:

Answer: (C) 44 + XY

• Reason: A human egg always carries an X chromosome (22 + X). If it is fertilized by a sperm carrying a Y chromosome (22 + Y), the resulting zygote will have 44 autosomes and the sex chromosome pair XY (totaling 46 chromosomes), which results in a male offspring.

7. The reasons for excessive generation of wastes are:

Answer: (C) (i), (ii), (iii) and (iv)

• Reason: All four points contribute to waste generation:

  1. Use and throw policy: Increases single-use item waste.

  2. Packaged food: Increases plastic and cardboard waste.

  3. Construction wastes: Contributes debris and industrial waste.

  4. Non-sorting: Makes recycling difficult, leading to more "mixed" waste reaching landfills.

8. Peristalsis in the Gut

• Assertion (A): The peristaltic movements occur all along the gut.

• Reason (R): The lining of the gut has muscles that contract rhythmically to push the food in a regulated manner.

Analysis: The assertion is True. Peristalsis starts in the esophagus and continues throughout the entire digestive tract (stomach and intestines). The reason is also True and explains how these movements happen: through the rhythmic contraction and relaxation of the smooth muscles in the gut wall.

Correct Option: (1) Both A and R are true, and R is the correct explanation of A.

9. Asexual Reproduction in Bacteria

• Assertion (A): Bacteria produced as a result of asexual reproduction would be similar.

• Reason (R): There would be only minor differences between the bacteria generated due to small inaccuracies in DNA replication.

Analysis: The assertion is True. In asexual reproduction (like binary fission), the offspring are essentially clones of the parent, making them very similar. The reason is also True. While the goal of DNA replication is to create an exact copy, slight chemical "errors" or mutations occur, leading to very minor variations. This correctly explains why they are similar but not always 100% identical.

Correct Option: (1) Both A and R are true, and R is the correct explanation of A.

10. (B) Plant Hormones (Phytohormones)
The specific plant hormones responsible for these processes are:

(i) Promote cell division: Cytokinins.

(ii) Inhibition of growth: Abscisic Acid (ABA).

(iii) Detection of light (Phototropism): Auxins (These hormones concentrate on the shaded side of a stem, causing cells to elongate and the plant to bend toward light).

(iv) Wilting of leaves: Abscisic Acid (ABA).

Section - B Chemistry

Question 17 Which of the following set of compounds does not belong to the same homologous series?

Correct Answer: (D) C₄H₈ and C₅H₁₂

Explanation:

A homologous series is a group of organic compounds that follow the same general formula.

• Options A, B, and C: All these compounds follow the general formula for alkanes: C_nH_2n+2.

  • CH₄ (Methane), C₂H₆ (Ethane), C₃H₈ (Propane), C₄H₁₀ (Butane), and C₅H₁₂ (Pentane) are all alkanes.

• Option D: * C₄H₈ follows the formula C_nH_2n, making it an alkene (Butene).

  • C₅H₁₂ follows the formula C_nH_2n+2, making it an alkane (Pentane).

  • Since they belong to different families (alkenes vs. alkanes), they do not belong to the same homologous series.

Question 18 Which of the following is an amphoteric oxide?

Correct Answer: (D) Al₂O₃

Explanation:

An amphoteric oxide is a metallic oxide that can react with both acids and bases to produce salt and water.

• Na₂O and K₂O (Options A & B): These are basic oxides (typical for Group 1 metals). They react with water to form strong bases.

• CO₂ (Option C): This is an acidic oxide (typical for non-metals). It reacts with water to form carbonic acid.

• Al₂O₃ (Option D): Aluminum oxide is a classic example of an amphoteric oxide. It can act as a base when reacting with a strong acid (like HCl) and as an acid when reacting with a strong base (like NaOH).

Question 19: Correct Answer: (C)

Question 17: Which of the following are combination reactions? - The correct option is (D) (ii) and (iii).

Question 18: A metal carbonate reacts with a solution X which forms a salt, water and a gas Y. What are X and Y? - Correct Answer: (C) X – Hydrochloric acid, Y – Carbon dioxide

Question 21: The pH of the gastric juices released during digestion is: Correct Answer: (A) Less than 7

Question 22: Baking powder is a mixture of: Correct Answer: (C) Sodium hydrogen carbonate + Tartaric acid

The volume ratio of hydrogen and oxygen gases liberated during electrolysis of water is: Correct Answer: (B) 2 : 1

Study the following table and select the correct option:Correct Answer: (D)

Question 22: Which of the following will not undergo addition reaction? - Correct Answer: (C) C3H8

Question 23: On reaction with dilute $HCl$, which of the following pair of metals will evolve hydrogen gas? : Correct Answer: (D)

Remaining Will Update soon

CBSE Class 10 Science Exam Pattern 2026

The CBSE Class 10 Science paper 2026 carried a total of 80 marks for theory and 20 marks for internal assessment, as per the latest CBSE exam pattern 2025–26. The Science paper is designed to test conceptual understanding, application-based learning, and competency-based skills in Physics, Chemistry, and Biology

Marking Scheme and Weightage

• Theory Exam: 80 marks

• Internal Assessment: 20 marks (periodic tests, practical work, projects, portfolio)

• Duration: 3 hours (10:30 AM – 1:30 PM)

According to the latest CBSE guidelines, the Science theory syllabus is divided into the following major units:

How to Use the CBSE Class 10 Science Unofficial Answer Key 2026

Once the unofficial answer key for CBSE Class 10 Science 2026 is published around 2:00 PM, students can follow these steps to calculate their expected marks

1. Keep your Science question paper and OMR/answer sheet with you.

2. Match your responses with the set-wise unofficial answer key provided by experts.​

3. For MCQs and assertion–reason questions, award 1 mark for each correct answer, without negative marking

4. For short and long answers, compare with detailed solutions to estimate partial marks based on CBSE marking scheme.

5. Add the scores section-wise (Physics, Chemistry, Biology) to get your total out of 80.

This will help you predict your performance before the official result declaration and identify areas of improvement for upcoming subjects.

CBSE Class 10 Science 2026 – Official Answer Key and Result

The answer key released at 2:00 PM will be unofficial and meant only for immediate reference. The official CBSE Class 10 Science answer key 2026 (if released publicly) will be provided later on the CBSE academic/board portal along with instructions for evaluation.

Final marks will be based on:

• Board evaluation as per the official marking scheme

• Theory (80 marks) + Internal assessment (20 marks).​

Students are advised not to panic if there is a slight mismatch between unofficial and official solutions, as examiners may follow step-wise marking and allow equivalent answers.