Science carries 80 marks in the CBSE Class 10 board exam. With 5 units and 16 chapters, knowing which questions to prioritise can save you 40+ hours of preparation. This guide lists the most-expected question types from each chapter based on the official CBSE blueprint and past 10 years of papers.
Chemical Substances: 25 marks | World of Living: 23 marks | Natural Phenomena: 12 marks | Effects of Current: 13 marks | Natural Resources: 7 marks
Unit 1 — Chemical Substances (25 marks)
Chapter 1: Chemical Reactions and Equations
3-mark questions (most expected):
- Write the balanced chemical equation for a double displacement reaction with an example
- Identify oxidation and reduction in: CuO + H₂ → Cu + H₂O
- What are rancidity and corrosion? How can each be prevented?
5-mark questions:
- Explain with diagram: combination, decomposition, displacement, double displacement, and redox reactions (one example each)
- A student placed iron nails in copper sulphate solution. Describe observations and explain using an equation
Key diagrams: Decomposition of lead nitrate / zinc + sulphuric acid apparatus setup
Chapter 2: Acids, Bases and Salts
3-mark questions:
- Why does dry HCl gas not turn blue litmus red, but HCl solution does?
- What is a universal indicator? Why is it used instead of litmus?
- Explain with example how salts are formed from acid-base neutralisation
5-mark questions:
- Explain the preparation, properties and uses of washing soda and baking soda
- What happens when: (a) sodium hydroxide reacts with HCl (b) calcium hydroxide reacts with CO₂ (c) sodium reacts with water?
Plaster of Paris, baking soda, and washing soda questions appear every year. Know their chemical names, formulae, and at least 2 uses each.
Chapter 3: Metals and Non-metals
3-mark questions:
- Why are metals good conductors while non-metals are not? Give one exception.
- What is the thermite reaction? Where is it used?
- Explain the activity series and its significance
5-mark questions:
- Describe the extraction of metals from their ores with a diagram
- Explain with examples: highly reactive metals, moderately reactive metals, least reactive metals — and their extraction methods
Must-know reactions: Na + O₂, Mg + O₂, Al + Fe₂O₃, Fe + CuSO₄
Chapter 4: Carbon and Its Compounds
3-mark questions:
- What is catenation? Why does carbon show catenation more than other elements?
- Distinguish between saturated and unsaturated hydrocarbons with examples
- What is saponification? Write the equation
5-mark questions:
- Draw structural formulae for: ethane, ethene, ethyne, ethanol, ethanoic acid
- Explain the properties of ethanol and ethanoic acid in detail
- What are the chemical properties of carbon compounds (combustion, addition, substitution)?
The structure of a soap micelle (how it cleans oil) is a frequent 3-mark diagram question. Practice drawing it.
Chapter 5: Periodic Classification
3-mark questions:
- What are the limitations of Mendeleev's periodic table? How did the Modern Periodic Table address them?
- How do atomic size, metallic character, and valency change across a period and down a group?
5-mark questions:
- Compare Döbereiner's triads, Newlands' octaves, and Mendeleev's table — limitations of each
Unit 2 — World of Living (23 marks)
Chapter 6: Life Processes
3-mark questions:
- Differentiate between aerobic and anaerobic respiration with equations
- Describe the process of photosynthesis with the equation
- What is the role of valves in the heart?
5-mark questions:
- Draw a labelled diagram of the human digestive system and explain each part's function
- Explain double circulation in humans with a diagram
Diagrams: Human heart (labelled), nephron, cross-section of leaf
Chapter 7: Control and Coordination
3-mark questions:
- What is a reflex arc? Draw a diagram showing components
- Distinguish between nervous and endocrine coordination
- Name the hormones secreted by the thyroid, adrenal, and pituitary glands and their functions
5-mark questions:
- Explain the structure and function of the human brain with a labelled diagram
- Describe how plants respond to external stimuli (phototropism, geotropism, hydrotropism, thigmotropism)
The reflex arc diagram and the human brain diagram appear in almost every year's paper. Memorise the labels.
Chapter 8: How Do Organisms Reproduce?
3-mark questions:
- Compare sexual and asexual reproduction — 3 differences
- Explain the process of fertilisation in flowering plants
- What are the methods of contraception? Classify them.
5-mark questions:
- Describe the male and female reproductive systems in humans with diagrams
- Explain vegetative propagation — advantages and examples
Chapter 9: Heredity and Evolution
3-mark questions:
- What is the significance of variation?
- Distinguish between acquired and inherited traits with examples
- What is speciation? When does it occur?
5-mark questions:
- Explain Mendel's laws using a monohybrid cross with a Punnett square
- Describe the evidence for evolution: homologous organs, analogous organs, fossils
Numericals: Punnett square for dihybrid crosses (TT × tt → Tt)
Unit 3 — Natural Phenomena (12 marks)
Chapter 10: Light — Reflection and Refraction
3-mark questions:
- State and explain the laws of refraction
- What is total internal reflection? What are its conditions?
- A concave mirror has a focal length of 15 cm. Find the image position for object at 45 cm.
5-mark questions:
- Explain with ray diagrams: image formation by a convex lens for object at different positions
- Distinguish between real and virtual images
Numericals: Mirror formula (1/v + 1/u = 1/f), magnification (m = −v/u), lens formula, power (P = 1/f)
Chapter 11: Human Eye and Colourful World
3-mark questions:
- What is the power of accommodation? Why does it decrease with age?
- Explain how a prism disperses white light
- Distinguish between myopia and hypermetropia — cause and correction
5-mark questions:
- Explain the atmospheric phenomena: blue colour of sky, red colour of sunrise/sunset, twinkling of stars
Unit 4 — Effects of Current (13 marks)
Chapter 12: Electricity
3-mark questions:
- State Ohm's law. Draw V-I graph for a metallic conductor.
- Derive the expression for equivalent resistance in series and parallel combinations
- What is the commercial unit of electrical energy? Convert to SI unit.
5-mark questions:
- Derive the formula for heat produced (H = I²Rt) and explain Joule's heating
- Explain the factors affecting resistance of a conductor
Numericals (very common):
- Find current when resistance and voltage are given
- Find equivalent resistance of mixed series-parallel circuits
- Calculate electrical energy consumed in kWh given power and time
Chapter 13: Magnetic Effects of Electric Current
3-mark questions:
- State Fleming's left-hand rule and right-hand rule — when is each used?
- What is electromagnetic induction? State Faraday's law.
- Describe the working of an AC generator with a diagram
5-mark questions:
- Explain the construction and working of an electric motor with diagram
- Describe the domestic electric circuit — why are appliances connected in parallel?
Unit 5 — Natural Resources (7 marks)
Chapter 14: Our Environment
3-mark questions:
- What is a food chain? Give an example of a terrestrial food chain with 4 levels.
- Explain how ozone is formed and destroyed. Why is ozone depletion a concern?
- Define biodegradable and non-biodegradable waste with 2 examples each
Chapter 15: Management of Natural Resources
3-mark questions:
- What is the 3R principle (Reduce, Reuse, Recycle)? Give one example of each.
- What is rainwater harvesting? Describe any one method.
- Why is biodiversity important? What are the main threats to it?
Last-Minute Focus List
Based on frequency of appearance in CBSE papers:
Chemistry (must revise): Balanced equations for all common reactions, pH scale, activity series, carbon compounds (ethanol + ethanoic acid)
Biology (must revise): Photosynthesis equation, double circulation diagram, reflex arc diagram, Mendel's laws with Punnett square
Physics (must revise): Mirror formula problems, Ohm's law numericals, series/parallel resistance, Fleming's rules, electromagnetic induction
CBSE board exams typically repeat 60-70% of question types from the previous 5 years. Solve past papers from 2019-2025 for maximum score impact.
Practice CBSE Class 10 Science chapter by chapter at JoyOfExams.in — adaptive questions that learn what you need to improve.