Looking for accurate SEBA Class 10 Science Chapter 1 (Chemical Reactions and Equations) textual solutions for the 2026–27 academic year? Access step-by-step exercise answers, balanced chemical equations, and clear explanations designed to help you score top marks in your HSLC board exams.
Exercise
Q1. Which of the following statements about the reaction below are incorrect? 2PbO(s) + C(s) → 2Pb(s) + CO2(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
A) (a) and (b)
B) (a) and (c)
C) (a), (b), and ©
D) All of the above
Answer: A) (a) and (b) Explanation: Lead oxide (PbO) is reduced to lead (Pb), and carbon (C) is oxidised to carbon dioxide (CO2). Therefore, statements (a) and (b) are incorrect.
Q2. Fe2O3 + 2Al → Al2O3 + 2Fe The above reaction is an example of a:
A) Combination reaction
B) Double displacement reaction
C) Decomposition reaction
D) Displacement reaction
Answer: D) Displacement reaction Explanation: Aluminium is more reactive than iron, so it displaces iron from iron(III) oxide.
Q3. What happens when dilute hydrochloric acid is added to iron filings?
A) Hydrogen gas and iron chloride are produced.
B) Chlorine gas and iron hydroxide are produced.
C) No reaction takes place.
D) Iron salt and water are produced.
Answer: A) Hydrogen gas and iron chloride are produced. Explanation: Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g)
Q4. What is a balanced chemical equation? Why should chemical equations be balanced?
Answer: A balanced chemical equation is an equation in which the total number of atoms of each element is equal on both the reactant and product sides.
Chemical equations must be balanced to satisfy the Law of Conservation of Mass, which states that mass can neither be created nor destroyed in a chemical reaction.
Q5. Translate the following statements into chemical equations and balance them:
(i) Hydrogen gas combines with nitrogen to form ammonia.
(ii) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(iii) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(iv) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Answer: (i) N2(g) + 3H2(g) → 2NH3(g)
(ii) 2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g)
(iii) 3BaCl2(aq) + Al2(SO4)3(aq) → 3BaSO4(s) + 2AlCl3(aq)
(iv) 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
SEBA Class 10 Science Chapter 1 Notes
Q6. Balance the following chemical equations:
(i) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(ii) NaOH + H2SO4 → Na2SO4 + H2O
(iii) NaCl + AgNO3 → AgCl + NaNO3
(iv) BaCl2 + H2SO4 → BaSO4 + HCl
Answer: (i) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(ii) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(iii) NaCl + AgNO3 → AgCl + NaNO3
(iv) BaCl2 + H2SO4 → BaSO4 + 2HCl
Q7. Write the balanced chemical equations for the following reactions:
(i) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(ii) Zinc + Silver nitrate → Zinc nitrate + Silver
(iii) Aluminium + Copper chloride → Aluminium chloride + Copper
(iv) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride
Answer: (i) Ca(OH)2 + CO2 → CaCO3 + H2O
(ii) Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
(iii) 2Al + 3CuCl2 → 2AlCl3 + 3Cu
(iv) BaCl2 + K2SO4 → BaSO4 + 2KCl
Q8. Write the balanced chemical equation and identify the type of reaction for each of the following:
(i) Potassium bromide + Barium iodide → Potassium iodide + Barium bromide
(ii) Zinc carbonate → Zinc oxide + Carbon dioxide
(iii) Hydrogen + Chlorine → Hydrogen chloride
(iv) Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen
Answer: (i) 2KBr(aq) + BaI2(aq) → 2KI(aq) + BaBr2(aq) Type: Double displacement reaction
(ii) ZnCO3(s) → ZnO(s) + CO2(g) Type: Decomposition reaction
(iii) H2(g) + Cl2(g) → 2HCl(g) Type: Combination reaction
(iv) Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) Type: Displacement reaction
Q9. What are exothermic and endothermic reactions? Give one example of each.
Answer: • Exothermic Reaction: A chemical reaction in which heat energy is released along with the products. Example: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + Heat
• Endothermic Reaction: A chemical reaction in which heat energy is absorbed from the surroundings. Example: CaCO3(s) + Heat → CaO(s) + CO2(g)
Q10. Why is respiration considered an exothermic reaction? Explain.
Answer: Respiration is considered an exothermic reaction because energy is released during the process. In this process, glucose combines with oxygen in our body cells to produce carbon dioxide, water, and energy.
Equation: C6H12O6(aq) + 6O2(g) → 6CO2(g) + 6H2O(l) + Energy
Chemical Reactions and Equations Class 10 SEBA Textual Exercise Solutions
11. Why are decomposition reactions called the opposite of combination reactions? Give equations.
Answer: Decomposition reactions are called the opposite of combination reactions because, in a combination reaction, two or more substances combine to form a single product, whereas in a decomposition reaction, a single compound breaks down into two or more simpler substances.
Combination reaction:
2H₂ + O₂ → 2H₂O
In this reaction, hydrogen and oxygen combine to form water.
Decomposition reaction:
2H₂O → 2H₂ + O₂
In this reaction, water breaks down into hydrogen and oxygen.
Therefore, decomposition reactions are opposite to combination reactions.
12. Give one decomposition reaction each carried out by heat, light and electricity.
Answer:
(a) Decomposition by Heat (Thermal Decomposition):
CaCO₃(s) → CaO(s) + CO₂(g)
In this reaction, calcium carbonate decomposes on heating.
(b) Decomposition by Light (Photolysis):
2AgCl(s) → 2Ag(s) + Cl₂(g)
In this reaction, silver chloride decomposes in the presence of sunlight.
(c) Decomposition by Electricity (Electrolysis):
2H₂O(l) → 2H₂(g) + O₂(g)
In this reaction, water decomposes into hydrogen and oxygen by passing electric current through it.
13. What is the difference between displacement and double displacement reactions? Give examples.
Answer:
| Displacement Reaction | Double Displacement Reaction |
| In a displacement reaction, a more reactive element displaces a less reactive element from its compound. | In a double displacement reaction, the ions of two compounds exchange their places to form new compounds. |
| General equation: A + BC → AC + B | General equation: AB + CD → AD + CB |
| Example: Zn + CuSO₄ → ZnSO₄ + Cu | Example: AgNO₃ + NaCl → AgCl + NaNO₃ |
14. How can silver be recovered from silver nitrate solution using copper?
Answer: Silver can be recovered from silver nitrate solution by adding copper metal to the solution. Copper displaces silver from silver nitrate because copper is more reactive than silver.
Chemical equation:
Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)
Silver is obtained as a solid deposit.
15. What is a precipitation reaction? Give an example.
Answer: A precipitation reaction is a chemical reaction in which an insoluble solid called a precipitate is formed when two aqueous solutions react.
Example:
AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
In this reaction, silver chloride (AgCl) is formed as a white precipitate.
SEBA Class 10 Science Chapter 1 Solutions
16. Explain oxidation and reduction in terms of gain or loss of oxygen. Give two examples each.
Answer:
(a) Oxidation:
Oxidation is the process in which a substance gains oxygen.
Examples:
- 2Mg + O₂ → 2MgO
In this reaction, magnesium gains oxygen and forms magnesium oxide. - 4Fe + 3O₂ → 2Fe₂O₃
In this reaction, iron gains oxygen and forms iron(III) oxide.
(b) Reduction:
Reduction is the process in which a substance loses oxygen.
Examples:
- CuO + H₂ → Cu + H₂O
In this reaction, copper oxide loses oxygen and is reduced to copper. - Fe₂O₃ + 3CO → 2Fe + 3CO₂
In this reaction, iron(III) oxide loses oxygen and is reduced to iron.
HSLC Science Chapter 1 Question Answer
17. An element X is a shiny brown metal. On heating in air, it becomes black. Identify X and explain the reaction.
Answer: The element X is Copper (Cu). Copper is a shiny reddish-brown metal.
When copper is heated in air, it reacts with oxygen and forms black copper(II) oxide.
Chemical equation:
2Cu + O₂ → 2CuO
In this reaction, copper gains oxygen and gets oxidised.
18. Why do we apply paint on iron articles?
Answer: Paint is applied on iron articles to prevent rusting. It forms a protective layer on the surface of iron and prevents contact with air and moisture.Thus, painting helps to protect iron from corrosion and increases its life.
19. Why are oil and fat-containing foods flushed with nitrogen?
Answer:Oil and fat-containing foods are flushed with nitrogen to prevent rancidity. Nitrogen does not react with food and keeps oxygen away from it. This helps the food remain fresh for a longer time.
20. Explain the following terms with one example each.
(a) Corrosion
Answer: Corrosion is the slow damage of a metal due to the action of air and moisture.
Example:
Rusting of iron is an example of corrosion.
Chemical equation:
4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O
(b) Rancidity
Answer: Rancidity is the spoilage of food containing fats and oils, which causes a bad smell and taste.
Example:
Butter or cooking oil left open for a long time becomes rancid.
This happens because fats and oils react with oxygen in the air.
Class 10 Science Chapter 1 Question Answer SEBA 2026-27
🔬 Updated Solutions Notice: This page features complete, step-by-step SEBA Class 10 Science Chapter 1 (Chemical Reactions and Equations) Textual Exercise Solutions updated for the 2026–27 academic session. All balanced chemical equations, reaction types, and conceptual explanations strictly follow the latest revised Assam Board (SEBA) textbook.
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