CBSE Class 10 Science: All Chapters Important Questions Science PDF (2025-2026)

Preparing for CBSE Class 10 Science for the 2025-2026 board exam 10 requires a structured approach focused on high-weightage topics, recurring question patterns, and rigorous NCERT conceptual clarity. Downloading and practicing a curated CBSE Class 10 All Chapters Important Questions Science PDF allows students to transition from passive reading to active, exam-oriented problem-solving. This guide outlines the chapter-wise conceptual framework, essential chemical reactions, physics formulas, biological diagrams, and fully solved board-standard questions aligned with the latest CBSE marking scheme.

Key Concepts and Chapter-Wise High-Yield Breakdown

The CBSE Science syllabus for Class 10 is systematically divided into three main disciplines: Chemical Substances – Nature and Behaviour, World of Living, and Natural Phenomena / Effects of Current. Below is the chapter-wise breakdown of foundational concepts that frequently appear in board exam 10.

1. Chemical Substances (Chapters 1 to 4)

• Chemical Reactions and Equations: Types of chemical reactions (combination, decomposition, displacement, double displacement, redox). Identification of oxidizing and reducing agents. Balancing redox reactions and observing precipitation and color changes (e.g., thermal decomposition of ferrous sulphate and lead nitrate).
• Acids, Bases, and Salts: pH scale applications in daily life, neutralization reactions, water of crystallization, and industrial preparation of chemicals from common salt: Sodium Hydroxide (Chlor-alkali process), Bleaching Powder ($CaOCl_2$), Baking Soda ($NaHCO_3$), Washing Soda ($Na_2CO_3 \cdot 10H_2O$), and Plaster of Paris ($CaSO_4 \cdot \frac{1}{2}H_2O$).
• Metals and Non-Metals: Reactivity series, ionic bond formation, properties of ionic compounds, metallurgy principles (roasting, calcination, electrolytic refining), thermite reaction, and corrosion prevention.
• Carbon and Its Compounds: Covalent bonding in carbon, versatile nature (catenation and tetravalency), homologous series, functional groups, IUPAC nomenclature, chemical properties (combustion, oxidation, addition, substitution), and the mechanisms of esterification, saponification, and cleansing action of soaps and detergents.

2. World of Living & Natural Resources (Chapters 5, 6, 7, 8, and 13)

• Life Processes: Autotrophic nutrition (photosynthesis light and dark reaction equations), heterotrophic nutrition, aerobic vs. anaerobic breakdown of glucose pathways, double circulation in humans (schematic flow through heart chambers), and excretory system structure (nephron ultrafiltration and selective reabsorption).
• Control and Coordination: Structure of neuron, transmission of nerve impulse, reflex arc pathway, human brain regions and their functions, and plant hormones (auxins, gibberellins, cytokinins, abscisic acid) along with tropic movements.
• How Do Organisms Reproduce?: Asexual reproduction modes (binary fission, budding, spore formation, regeneration, vegetative propagation), sexual reproduction in flowering plants (pollination to fertilization and seed formation), and human male/female reproductive systems with contraceptive methods.
• Heredity: Mendel’s monohybrid cross ($3:1$ phenotypic ratio, $1:2:1$ genotypic ratio) and dihybrid cross ($9:3:3:1$ ratio), laws of inheritance, and sex determination mechanism in human beings ($XX/XY$ chromosome system).
• Our Environment: Ecosystem trophic levels, 10% law of energy transfer, biological magnification of non-biodegradable pesticides, ozone layer depletion mechanisms ($CFCs$), and solid waste management.

3. Natural Phenomena & Effects of Current (Chapters 9 to 12)

• Light – Reflection and Refraction: Laws of reflection and refraction, mirror formula, lens formula, magnification conventions, Snell’s law, refractive index ($n = c/v$), and standard ray diagrams for concave/convex mirrors and spherical lenses.
• The Human Eye and the Colourful World: Defects of vision (myopia, hypermetropia, presbyopia) with ray diagrams for correction using concave/convex lenses, dispersion of white light through a glass prism, atmospheric refraction (twinkling of stars, advance sunrise), and scattering of light (Tyndall effect, blue sky colour).
• Electricity: Electric current ($I = Q/t$), electric potential difference ($V = W/Q$), Ohm’s law ($V = IR$), factors affecting resistance ($R = \rho \frac{l}{A}$), series and parallel resistor combinations, Joule’s law of heating ($H = I^2Rt$), and electrical power ($P = VI = I^2R = \frac{V^2}{R}$).
• Magnetic Effects of Electric Current: Magnetic field lines and their properties, right-hand thumb rule, magnetic field due to a straight conductor, circular loop, and solenoid, Fleming’s left-hand rule, and domestic electric circuits (earthing, short circuiting, overloading).

Detailed Concept Explanation: Equations and Formulas

To score full marks in numerical and chemical equation questions in CBSE Class 10 Science, students must present precise step-by-step mathematical working and state symbols.

1. Quantitative Physics: Circuit Analysis and Power Dissipation

In electrical circuits containing combinations of resistors, equivalent resistance and power dissipation are calculated using the following fundamental relationships:

• Equivalent Resistance in Series: $R_s = R_1 + R_2 + R_3 + \dots + R_n$
• Equivalent Resistance in Parallel: $\frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \dots + \frac{1}{R_n}$
• Electric Power Formulae: $P = V \times I = I^2R = \frac{V^2}{R}$ (Unit: Watt, $W$)
• Commercial Unit of Electrical Energy: $1\text{ kWh} = 1\text{ unit} = 3.6 \times 10^6\text{ Joules (J)}$

2. Organic Chemical Reactions: Esterification vs. Saponification

These two complementary reactions are heavily emphasized in CBSE board examinations:

1. Esterification: Ethanoic acid reacts with absolute ethanol in the presence of concentrated sulphuric acid ($H_2SO_4$) as a catalyst to form a sweet-smelling ester (ethyl ethanoate):
   $\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{conc. } \text{H}_2\text{SO}_4} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$
2. Saponification: When an ester reacts with a base such as sodium hydroxide ($NaOH$), it converts back into sodium ethanoate (soap) and ethanol:
   $\text{CH}_3\text{COOC}_2\text{H}_5 + \text{NaOH} \rightarrow \text{CH}_3\text{COONa} + \text{C}_2\text{H}_5\text{OH}$

Important CBSE Questions with Step-by-Step Answers

Below are representative high-yield questions from the official CBSE question bank pattern with detailed solutions aligned with board marking schemes.

Question 1 (Chemistry – 3 Marks)

Question: A reddish-brown metal ‘X’ on heating in air gives a black compound ‘Y’. When hydrogen gas is passed over heated ‘Y’, it turns back into ‘X’.

1. Identify ‘X’ and ‘Y’.
2. Write balanced chemical equations for both reactions with state symbols.
3. Identify the substance oxidized and reduced in the second reaction.

Answer:

1. Metal ‘X’ is Copper ($\text{Cu}$). Black compound ‘Y’ is Copper(II) Oxide ($\text{CuO}$).
2. Reaction 1 (Oxidation of Copper):
   $2\text{Cu(s)} + \text{O}_2\text{(g)} \xrightarrow{\Delta} 2\text{CuO(s)}$
   Reaction 2 (Reduction of Copper Oxide):
   $\text{CuO(s)} + \text{H}_2\text{(g)} \xrightarrow{\Delta} \text{Cu(s)} + \text{H}_2\text{O(g)}$
3. In the second reaction:
   • Substance Oxidized: $\text{H}_2$ (gains oxygen to form $\text{H}_2\text{O}$)
   • Substance Reduced: $\text{CuO}$ (loses oxygen to form $\text{Cu}$)

Question 2 (Biology – 3 Marks)

Question: Explain the three different pathways of glucose breakdown in living organisms. Mention the site of each pathway and the end products formed.

Answer:

In all organisms, glucose (a 6-carbon molecule) is first converted into Pyruvate (a 3-carbon molecule) plus energy in the cytoplasm (Glycolysis). Further breakdown occurs via three pathways:

1. Anaerobic Pathway in Yeast (Fermentation): Takes place in the absence of oxygen. Pyruvate is converted into Ethanol + Carbon Dioxide + Energy (2 ATP).
2. Anaerobic Pathway in Muscle Cells: Occurs during sudden or strenuous physical activity under lack of oxygen. Pyruvate is converted into Lactic Acid + Energy. Accumulation of lactic acid causes muscle cramps.
3. Aerobic Pathway in Mitochondria: Takes place in the presence of oxygen. Pyruvate is completely broken down into $\text{CO}_2$ + $\text{H}_2\text{O}$ + Energy (36–38 ATP), releasing significantly higher energy than anaerobic pathways.

Question 3 (Physics – 5 Marks)

Question: An object $4\text{ cm}$ in size is placed at a distance of $25\text{ cm}$ in front of a concave mirror of focal length $15\text{ cm}$.

1. At what distance from the mirror should a screen be placed in order to obtain a sharp image?
2. Find the nature and size of the image formed.
3. Draw a neat ray diagram showing the image formation.

Answer:

Given (according to Cartesian sign convention):

• Height of object, $h_o = +4\text{ cm}$
• Object distance, $u = -25\text{ cm}$
• Focal length of concave mirror, $f = -15\text{ cm}$

Step 1: Using the Mirror Formula:

$\frac{1}{f} = \frac{1}{v} + \frac{1}{u} \implies \frac{1}{v} = \frac{1}{f} - \frac{1}{u}$

$\frac{1}{v} = \frac{1}{-15} - \frac{1}{-25} = -\frac{1}{15} + \frac{1}{25} = \frac{-5 + 3}{75} = \frac{-2}{75}$

$v = -\frac{75}{2} = -37.5\text{ cm}$

Conclusion: The screen should be placed at a distance of $37.5\text{ cm}$ in front of the mirror (on the same side as the object).

Step 2: Calculating Image Height and Nature:

$m = -\frac{v}{u} = \frac{h_i}{h_o} \implies h_i = -\frac{v}{u} \times h_o$

$h_i = -\left(\frac{-37.5}{-25}\right) \times 4 = -(1.5) \times 4 = -6\text{ cm}$

Nature of image: Real, inverted, and magnified ($h_i = -6\text{ cm}$, lying beyond the Center of Curvature $C$).

Question 4 (Physics – 3 Marks)

Question: An electric lamp of resistance $20\text{ }\Omega$ and a conductor of $4\text{ }\Omega$ resistance are connected in series to a $6\text{ V}$ battery. Calculate: (a) Total resistance of the circuit, (b) Overall current flowing through the circuit, (c) Potential difference across the electric lamp and the conductor.

Answer:

1. Total Resistance ($R_s$):
   Since components are connected in series:
   $R_s = R_1 + R_2 = 20\text{ }\Omega + 4\text{ }\Omega = 24\text{ }\Omega$
2. Current through circuit ($I$):
   Using Ohm’s Law ($I = \frac{V}{R_s}$):
   $I = \frac{6\text{ V}}{24\text{ }\Omega} = 0.25\text{ A}$
3. Potential Difference across individual components:
   Across the lamp ($V_1$): $V_1 = I \times R_1 = 0.25\text{ A} \times 20\text{ }\Omega = 5\text{ V}$
   Across the conductor ($V_2$): $V_2 = I \times R_2 = 0.25\text{ A} \times 4\text{ }\Omega = 1\text{ V}$
   Verification: $V_1 + V_2 = 5\text{ V} + 1\text{ V} = 6\text{ V}$ (equals battery voltage).

Question 5 (Biology – 2 Marks)

Question: Why is the flow of energy in an ecosystem unidirectional? Explain with reference to Lindeman’s 10% law.

Answer:

The energy flow in an ecosystem is always unidirectional because energy captured by autotrophs from sunlight does not revert back to solar input, and energy passed to herbivores cannot return to producers. According to the 10% Law, only about 10% of the energy available at a particular trophic level is transferred to the next higher level. The remaining 90% is lost to the environment as heat and utilized in life metabolic processes (respiration, digestion, growth). Consequently, available energy decreases progressively at higher trophic levels, limiting food chains to 3–4 steps.

How to Prepare for CBSE Class 10 Science Board Exam

To maximize your score in the CBSE Class 10 Science board examination, follow these strategic preparation guidelines:

1. Master NCERT In-Text Questions & Exemplars: Nearly 85% of theoretical and numerical problems in the board examination originate directly or with slight numerical modifications from NCERT textbook exercises and NCERT Exemplar questions.
2. Practice Labeled Diagrams Regularly: Essential diagrams carry dedicated marks in Biology and Physics. Practice drawing the human alimentary canal, heart schematic, excretory system (nephron), reflex arc, female reproductive system, and optical ray diagrams for lenses and mirrors.
3. Memorize Standard Chemical Reactions and Conditions: Maintain a formula sheet for decomposition reactions, metal reactivity series, salt preparations, and carbon reactions with specific temperature and catalyst requirements.
4. Strictly Follow Cartesian Sign Conventions: When solving optics numericals, always define signs before substitution ($u$ is always negative, focal length $f$ of concave mirror/lens is negative, convex mirror/lens is positive).
5. Solve Competency-Based and Assertion-Reason Questions: Under the 2025-2026 assessment framework, 50% of the question paper comprises competency-focused questions (case-based scenarios, assertion-reason, and data-interpretation MCQs).

Where to Practice More

Consistent practice with time-bound question papers is the key differentiator for scoring 95%+ in board examinations. Access comprehensive test preparation resources on Theorify QPTool to test your conceptual accuracy.

Explore the complete chapter-wise question collections and customized question papers on the CBSE Class 10 Science Question Bank, and assess your examination readiness with timed CBSE Class 10 Science Sample Papers with instant marking scheme solutions.