Chapter 1: Chemical Reactions and Equations

VVI questions — the ones the board asked most (17)

1. Q1Short answer5 marksAsked: 2023

   What is a chemical equation ? What information are obtained from the following equation ? 2SO2 + O2 -> 2SO3

   

   Medha Ma’am

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   Model answer · chemical equation, balanced equation information

   1. 1.Representing a chemical reaction in a concise form using symbols and formulas is called a chemical equation.1 mark
   2. 2.The equation 2SO2 + O2 → 2SO3 indicates that sulfur dioxide (SO2) and oxygen (O2) react together to form sulfur trioxide (SO3).1 mark
   3. 3.According to this equation, two moles of sulfur dioxide and one mole of oxygen participate in the reaction.1 mark
   4. 4.As a result of this reaction, two moles of sulfur trioxide are obtained as the product.1 mark
   5. 5.This equation shows that mass is conserved in the reaction, because the number of atoms of sulfur and oxygen is equal on both sides of the equation, that is, the equation is balanced.1 mark

   • Begin with the exact book definition: 'Representing a chemical reaction in a concise form using symbols and formulas is called a chemical equation.'
   • Name SO2, O2 and SO3 while explaining the reaction so this point is clearly earned.
   • State the mole amounts of reactants and product separately, then explain balancing shows mass is conserved because atoms are equal on both sides.

   Marks split from a structure derived from past papers (checked twice); not Bihar Board’s official scheme

2. Q2Short answer2 marksAsked: 2021

   What is a combination reaction?

   

   Medha Ma’am

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   Hear it from Medha Ma’am · 25 s

   Model answer · combination reaction

   1. 1.A combination reaction is a chemical reaction in which two or more substances combine to form a single product.1 mark
   2. 2.For example, calcium oxide and water combine to form a single product, calcium hydroxide, as represented by the equation CaO(s) + H2O(l) → Ca(OH)2(aq).1 mark

   • Write the exact phrase 'single product' and 'two or more' while defining combination reaction.
   • Write the equation CaO(s) + H2O(l) → Ca(OH)2(aq) with state symbols as the example.
   • Do not add extra examples or explanations beyond the definition and one equation.

   Marks split from a structure derived from past papers (checked twice); not Bihar Board’s official scheme

3. Q3Short answer2 marksAsked: 2024

   Write the balanced chemical equations for the following reactions : (a) Zinc + Silver nitrate -> Zinc nitrate + Silver (b) Sodium + Water -> Sodium hydroxide + Hydrogen

   

   Medha Ma’am

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   Hear it from Medha Ma’am · 35 s

   Model answer · balancing chemical equations, displacement and combination reactions

   1. 1.The balanced chemical equation for zinc reacting with silver nitrate is Zn + 2AgNO3 → Zn(NO3)2 + 2Ag.1 mark
   2. 2.The balanced chemical equation for sodium reacting with water is 2Na + 2H2O → 2NaOH + H2.1 mark

   • Write Zn(NO3)2 with the correct subscript 2 and balance Ag with coefficient 2.
   • Write 2Na and 2H2O on the left and 2NaOH and H2 on the right, not just Na + H2O.
   • Keep both equations on separate lines, each with an arrow (→) and no extra words.

   Marks split from a structure derived from past papers (checked twice); not Bihar Board’s official scheme

4. Q4Short answer2 marksAsked: 2024

   What is the difference between displacement and double displacement reactions ? Write equations for these reactions.

   How the model answer begins

   1. In a displacement reaction, a more reactive element displaces a less reactive element from its compound.

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5. Q5Short answer2 marksAsked: 2025

   Write three information obtained from chemical equation.

   How the model answer begins

   1. A chemical equation provides information about the names and chemical formulas of reactants and products taking part in a reaction.

   The full answer from Medha Ma’am →
6. Q6Short answer2 marksAsked: 2025

   Why does the colour of the solution change when a piece of iron is added to copper sulphate solution?

   How the model answer begins

   1. Iron displaces copper from the copper sulphate solution because iron is more reactive than copper. The reaction taking place is Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s). In this reaction, iron has displaced or removed…

   The full answer from Medha Ma’am →
7. Q7Short answer2 marksAsked: 2026

   Describe a precipitation reaction with an example.

   How the model answer begins

   1. A precipitation reaction is a chemical reaction in which an insoluble substance, called a precipitate, is formed. Any reaction that produces a precipitate can be called a precipitation reaction.

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8. Q8Short answer2 marksAsked: 2026

   What are oxidation-reduction reactions ?

   How the model answer begins

   1. Oxidation is a chemical reaction in which oxygen is added or hydrogen is removed from a substance.

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9. Q9Short answer2 marksAsked: 2026

   Explain the process of extinguishing fire using a fire extinguisher through a chemical reaction.

   How the model answer begins

   1. In a fire extinguisher, sodium bicarbonate reacts with dilute sulphuric acid, and this reaction produces carbon dioxide gas, which extinguishes the fire.

   The full answer from Medha Ma’am →
10. Q10Short answer2 marksAsked: 2026

    What is a balanced chemical equation ? Give an example.

    How the model answer begins

    1. A balanced chemical equation is a chemical equation in which the number of atoms of each element in the reactants and products is equal.

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11. Q11Short answer2 marksAsked: 2023

    Identify the substances that are oxidised and reduced in the following reactions :- i) 4Na (s) + O2 (g) -> 2Na2O (s) ii) CuO (s) + H2 (g) -> Cu (s) + H2O (l)

    How the model answer begins

    1. In reaction (i), 4Na(s) + O2(g) → 2Na2O(s), Sodium (Na) is oxidised because oxygen is added to it to form Na2O.

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12. Q12Short answer2 marksAsked: 2022

    Write the balanced chemical equations for the following reactions : (i) Zinc (s) + Sulphuric acid (aq) -> Zinc sulphate (aq) + Hydrogen (g) (ii) Barium chloride (aq) + Sulphuric acid (aq) -> Barium sulphate (s) + Hydrochloric acid (aq)

    How the model answer begins

    1. Zinc reacts with sulphuric acid to give zinc sulphate and hydrogen gas. The balanced chemical equation is: Zn + H2SO4 → ZnSO4 + H2

    The full answer from Medha Ma’am →
13. Q13Short answer2 marksAsked: 2022

    What is a balanced chemical equation ? Write the balanced form of the following equation : Al(s) + H2SO4(aq) -> Al2(SO4)3(aq) + H2(g)

    How the model answer begins

    1. A balanced chemical equation is a chemical equation in which the number of atoms of each element in the reactants and products is equal. In other words, the number of atoms of each element remains the same before and…

    The full answer from Medha Ma’am →
14. Q14Short answer2 marksAsked: 2022

    On heating copper turnings in air for a long time, a black coating is formed on it. On passing hydrogen gas over it, its brown colour reappears. What are the reactions taking place here? Write the names of the reactions and the equations.

    How the model answer begins

    1. When copper turnings are heated in air for a long time, oxygen is added to copper and a black coating of copper(II) oxide is formed on the surface. This reaction is called an oxidation reaction, given as: 2Cu + O2…

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15. Q15Short answer2 marksAsked: 2021

    What is rancidity ? Explain with example.

    How the model answer begins

    1. Rancidity is the process in which fats and oils present in food materials get oxidised when left for a long time, due to which their smell and taste change.

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16. Q16Short answer2 marksAsked: 2025

    Write three information obtained from chemical equation.

    How the model answer begins

    1. A chemical equation provides information about the names and chemical formulae of the reactants and products involved in the reaction.

    The full answer from Medha Ma’am →
17. Q17Short answer2 marksAsked: 2022

    When copper shavings are heated in air for a long time, a black layer is formed on it. On passing hydrogen gas over it, its brown colour returns. Which reactions take place here? Write the names and equations of the reactions.

    How the model answer begins

    1. When copper shavings are heated in air for a long time, oxygen is added to copper and copper oxide is formed. Since the substance copper gains oxygen during this reaction, it is an oxidation reaction.

    The full answer from Medha Ma’am →

Objective questions with the board’s key (10)

1. 1. Bihar Board 2026

   The chemical reaction, Na_2SO_4(aq) + BaCl_2(aq) -> BaSO_4(s) + 2NaCl(aq) is of which type ?

   • (A) Combination reaction
   • (B) Double displacement reaction ✓
   • (C) Decomposition reaction
   • (D) Displacement reaction

   Answer: (B)

2. 2. Bihar Board 2026

   The addition of oxygen to a substance during a chemical reaction is called

   • (A) reduction
   • (B) oxidation ✓
   • (C) corrosion
   • (D) none of these

   Answer: (B)

3. 3. Bihar Board 2026

   The ratio of numbers of atoms of hydrogen and oxygen in water is

   • (A) 2 : 1 ✓
   • (B) 2 : 2
   • (C) 1 : 2
   • (D) 1 : 1

   Answer: (A)

4. 4. Bihar Board 2026

   Which of the following reactions takes place in the conversion of milk into curd ?

   • (A) Decomposition
   • (B) Photosynthesis
   • (C) Fermentation ✓
   • (D) Excretion

   Answer: (C)

5. 5. Bihar Board 2026

   Which of the following solutions is used for whitewashing of wall ?

   • (A) Ca(HCO3)2
   • (B) Ca(OH)2 ✓
   • (C) CaCO3
   • (D) Ca

   Answer: (B)

6. 6. Bihar Board 2026

   The chemical reaction, Na2SO4(aq) + BaCl2(aq) -> BaSO4(s) + 2NaCl(aq) is of which type ?

   • (A) Combination reaction
   • (B) Double displacement reaction ✓
   • (C) Decomposition reaction
   • (D) Displacement reaction

   Answer: (B)

7. 7. Bihar Board 2026

   The reaction in which heat is evolved along with the formation of products is called

   • (A) exothermic ✓
   • (B) endothermic
   • (C) photosynthesis
   • (D) oxidation

   Answer: (A)

8. 8. Bihar Board 2026

   The reaction 2Cu + O_2 -> 2CuO is which type of chemical reaction ?

   • (A) Oxidation ✓
   • (B) Reduction
   • (C) Displacement
   • (D) Neutralization

   Answer: (A)

9. 9. Bihar Board 2026

   Which of the following is an oxidant ?

   • (A) H_2
   • (B) CO
   • (C) O_3 ✓
   • (D) H_2S

   Answer: (C)

10. 10. Bihar Board 2026

    Which of the following is slaked lime ?

    • (A) CaO
    • (B) Ca(OH)2 ✓
    • (C) CaCO3
    • (D) Ca

    Answer: (B)

Questions parents and students ask

How many marks does "Chemical Reactions and Equations" carry in Bihar Board Class 10 Science?

In the Bihar Board papers of 2021–2026, this chapter carried about 4 marks and about 5 questions a year; by marks it ranks 11 in Science.

Which are the most important (VVI) questions of "Chemical Reactions and Equations"?

The 17 questions above are from the board’s real papers, each with the years it was asked; the most-asked come first with their full model answers. All 17 written questions of this chapter, with answers, are in the AskMedha app.

Do the answers follow the board’s marking scheme?

BSEB does not publish a marking scheme. Each answer is written point by point on a structure derived from past papers and checked by a second, independent model; it is never called the board’s official scheme.