NIOS Class 10 Science and Technology Chapter 4 Chemical Reaction and Equations

NIOS Class 10 Science and Technology Chapter 4 Chemical Reaction and Equations Solutions to each chapter is provided in the list so that you can easily browse through different chapters NIOS Class 10 Science and Technology Chapter 4 Chemical Reaction and Equations and select need one. NIOS Class 10 Science and Technology Chapter 4 Chemical Reaction and Equations Question Answers Download PDF. NIOS Study Material of Class 10 Science and Technology Notes Paper 212.

NIOS Class 10 Science and Technology Chapter 4 Chemical Reaction and Equations

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Also, you can read the NIOS book online in these sections Solutions by Expert Teachers as per National Institute of Open Schooling (NIOS) Book guidelines. These solutions are part of NIOS All Subject Solutions. Here we have given NIOS Class 10 Science and Technology Chapter 4 Chemical Reaction and Equations, NIOS Secondary Course Science and Technology Solutions for All Chapters, You can practice these here.

Chemical Reaction and Equations

Chapter: 4


1. Write a chemical equation for each of the following reactions: 

(i) Zinc metal reacts with aqueous hydrochloric acid to produce a solution of zinc chloride and hydrogen gas.

Ans: The balanced chemical equation for the reaction between zinc metal and aqueous hydrochloric acid is:


(ii) When solid mercury(II) oxide is heated, liquid mercury and oxygen gas are produced.

Ans: The balanced chemical equation for the reaction when solid mercury(II) oxide (HgO) is heated to produce liquid mercury ( Hg) and oxygen gas (O2) is: 


2. Balance the following chemical equations: 

(i) H2SO4 (aq) + NaOH (aq) ⎯⎯→ Na2SO4 (aq) + H2O (l).

Ans: H2SO4 + 2NaOH ⎯→Na2SO4.

(ii) Al (s) + HCl (aq) ⎯⎯→ AlCl3 (aq) + H2 (g).

Ans: 2AL+ 6HCL-2ALC13 +3H2.

3. What is a balanced chemical equation? Why should a chemical equation be balanced? 

Ans: The representation of the reaction between the two different compounds or the same compound dissociated with various elements are represented by the chemical equation. 

As we know from the laws of conservative of mass that the mass of reactants and products will be the same after any reaction so all the equations of chemical reaction will be balanced after the reaction.


1. Examine the following reaction(s) and identify which of them are not example(s) of a redox reaction?

(i) AgNO3 (aq) + HCl (aq) ⎯⎯→ AgCl (s) + HNO3 (aq).

Ans: AgNO3(aq) + HCl (aq) ⎯⎯→ AgCl(s) + HNO3(aq).

(ii) MnO2 (s) + 4HCl (aq) ⎯⎯→ MnCl2 (aq) + 2H2O (l) + Cl2 (g).

Ans: H2 is oxidised and CuO is reduced.

(iii) 4Na (s) + O2 (g) ⎯⎯→ 2Na2O (s). 

Ans: Zn is oxidised and Ag+ (in AgNO3) is reduced.


1. Write chemical equations of the following and balance them:

(i) Carbon + oxygen ⎯⎯→ Carbon dioxide.

Ans: The chemical reaction is, C +O2 —–> CO2.

(ii) Hydrogen + Chlorine ⎯⎯→ Hydrogen chloride.

Ans:  H2 + 2Cl —–> 2HCl.

(iii) Barium + Sodium ⎯⎯→ Barium + sodium. chloride sulphate sulphate chloride.

Ans: BaCl2 + Na2SO4 ——> BaSO4 + 2NaCl.

B. Write balanced chemical equations with physical state symbols and necessary conditions, if any: 

(i) Nitrogen reacts with hydrogen in the presence of iron as a catalyst at 200 atmospheric pressure and 600°C temperature, and the product obtained is ammonia.

Ans: N2(g) + 3 H2(g) 2NH3(g).

(ii) Aqueous solution of sodium hydroxide reacts with hydrochloric acid and produces sodium chloride and water. 

Ans: NaOH(g) + HCl(l) —–> NaCl(s) + H2O(l).

(iii) Phosphorus burns in chlorine gas to form phosphorus pentachloride.

​Ans: P4 (g) + 20Cl(g) —-> 4PCl5(g).

C. Balance the following chemical reactions:

(i) Ca(OH)2 + HNO3 ⎯→ Ca(NO3)2 + H2O.

Ans:  Ca(OH)2 + 2HNO3 ⎯→ Ca(NO3)2 + 2H2O.

(ii) BaCl2 (aq) + H2SO4 (aq) ⎯→ BaSO4 (s) + HCl (aq).

Ans: BaCl2 + H2SO4 ⎯→ BaSO4 + 2HCl. 

(iii) CuSO4 (aq) + Zn (s) ⎯→ ZnSO4 (aq) + Cu (s).

Ans:  CuSO4 + Zn ⎯→ ZnSO4 + Cu.

(iv) H2S (g) + SO2 (g) ⎯→ S (s) + H2O (l).

Ans:  H2S + SO2 ⎯→ 2S + H2O.

(v) BaCl2 (aq) + Al2(SO4)3 (aq) ⎯→ AlCl3 (aq) + BaSO4 (s).

Ans: 3BaCl2 + Al2(SO4)3  2AlCl3 + 3BaSO4.

(vi) Pb (NO3)2 (aq) + Fe2(SO4) (aq) ⎯→ Fe(NO3)3 (aq) + PbSO4 (s).

Ans: 3Pb(NO3)2 + Fe2(SO4)3  2Fe(NO3)3 + 3PbSO4.

(vii) Calcium hydroxide + carbon dioxide ⎯→ Calcium carbonate + water.

Ans: – Ca(OH)2 + CO2 ⎯→ CaCO3 + H2O.

(viii) Aluminium + Copper (II) chloride ⎯→ Aluminium chloride + copper.

Ans:  Al + 3CuCl2 ⎯→ AlCl3 + 3Cu.

(ix) Calcium carbonate + hydrochloric acid ⎯→ Calcium chloride + water + carbon dioxide.

Ans: CaCO3 + 2 HCl CaCl2 + H2O + CO2.

2. What is a balanced chemical equation? Write 3 characteristics of a balanced chemical equation?

Ans: A balanced chemical equation is a representation of a chemical reaction where the number of atoms of each element is the same on both the reactant and product sides. It follows the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction, only rearranged. 

There are 3 characteristics of a balanced chemical equations are mentioned below: 

(a) It denotes the different oxidation states of different elements that participate in the reaction.

(b) The property of that element or compound would be known to us.

(c) The valency of that molecule is known to us.

3. In what way is a displacement reaction different from a double-displacement reaction? Explain with two suitable examples.

Ans: Displacement reactions and double-displacement reactions are both types of chemical reactions, but they involve different mechanisms of rearranging atoms or ions. In a displacement reaction, an element displaces another element from a compound to form a new compound and release a free element.

Example: Zn+2HCl→ZnCl2+H2.

Another example: Fe+CuSO4→FeSO4+Cu.

4. What happens when dilute hydrochloric acid is added to iron filings? Mark (√) at the correct answer from the following.

(a) Hydrogen gas and iron chloride are produced and are classified as a displacement reaction.

(b) Iron chloride and chlorine gas are produced and are classified as a decomposition reaction.

(c) Iron hydroxide and water are produced and are classified as a combination reaction. 

(d) No reaction takes place but is classified as a double displacement reaction.

Ans: (a) Hydrogen gas and iron chloride are produced and are classified as a displacement reaction.

5. What do you mean by an exothermic reaction? Give a suitable example.

Ans: An exothermic reaction is a reaction in which energy is released in the form of light or heat. Thus in an exothermic reaction, energy is transferred into the surroundings rather than taking energy from the surroundings as in an endothermic reaction.

Example: C +O2 ⎯→ CO2 + Heat.

6. Classify each of the following reactions as combination, decomposition, displacement or double displacement reactions:

(a) Zn (s) + 2AgNO3 (aq) ⎯⎯→ Zn(NO3)2 + 2Ag (s).

Ans: Displacement reaction.

(b) 2KNO3 (s) heat ⎯⎯⎯→ 2KNO2 + O2 (g).

Ans: Displacement reaction.

(c) Ni (NO3)2 (aq) + 2NaOH (aq) ⎯⎯→ Ni(OH)2 (s) + 2NaNO3 (aq).

Ans: Double displacement reaction.

(d) 2KClO3 (s) heat ⎯⎯⎯→ 2KCl (s) + 3O2 (g).

Ans: Double displacement reaction.

(e) MgO (s) + C (s) ⎯⎯→ CO (g) + Mg (s).

Ans: Combination reaction. 

7. What is the difference between a combination and a decomposition reaction? Illustrate with suitable examples.

Ans: The difference between a combination and a decomposition reaction are mentioned below: 

Combination Reaction:

A combination reaction, also known as a synthesis reaction, occurs when two or more substances combine to form a single product.The general form of a combination reaction can be represented as: A + B → AB This type of reaction is characterised by the coming together of two or more substances to form a more complex compound.

Example: 2H2 (g)+O2 (g)→2H 2O(l)

Decomposition Reaction:

A decomposition reaction involves the breakdown of a single compound into two or more simpler substances. Generally represented by the equation: 𝐴𝐵→𝐴+𝐵 Decomposition reactions can be triggered by heat, light, electricity, or the addition of another substance. 

Example: 2H2​o (l) g     O(l)→2H 2 (g)+O 2 (g).Here, water (H₂O) decomposes into hydrogen gas (H₂) and oxygen gas (O₂) when an electric current is passed through it.

8. Is there any oxidation without reduction? Justify your answer.

Ans: No oxidation cannot without reduction. 

Definition of Oxidation and Reduction:

(i) Oxidation: It is defined as the loss of electrons by an atom or a molecule.

(ii) Reduction: It is defined as the gain of electrons by an atom or a molecule.

9. ‘Both combination reaction and displacement reaction fall in the category of redox reactions’. Do you agree? If so, discuss this aspect with suitable examples.

Ans: A combination reaction is a type of redox reaction. In a combination reaction, two components are combined to produce a single product. Displacement reaction is also a redox reaction, as the less reactive reactant is reduced and the more reactive reactant is oxidised in this reaction.

10. Give two examples from everyday life situations where redox reaction takes place. How will you prove it?

Ans: The example of everyday life situation of redox reaction are:

(i) Rancidity of different food items.

(ii) Corrosion in iron.

11. In the following reactions name the substances which are oxidised and reduced and also mention the oxidising and reducing agents.

(a) Ca (s) + Cl2 (g) heat ⎯⎯⎯→ CaCl2 (s).

Ans: In this reaction, Ca is oxidised so it is a reducing agent. And Cl is reduced then it is an oxidised agent.

(b) 3MnO2 (s) + 4Al (s) heat ⎯⎯⎯→ 3Mn (l) + 2Al2O3 (s).

Ans: In the upper reaction, Al is oxidised so it is a reducing agent. And MnO2 is reduced so it is an oxidizing agent.

(c) Fe2O3 (s) + 3CO (g) heat ⎯⎯⎯→ 2Fe (s) + 3CO2 (g).

Ans: Here CO is oxidised so it will be a reducing agent and Fe2O3 is reduced so it will be an oxidising agent. 

12. Explain the following in terms of electron transfer.

(a) Oxidation.

Ans: Oxidation: Oxidation occurs when an atom, ion, or molecule loses one or more electrons. In other words, it involves the increase in the oxidation state of an atom or a molecule. Think of it as “loss of electrons.

(b) Reduction.

Ans: It is a process in which oxygen is looses or hydrogen is gain by the element or the compound.

13. What is the law of definite proportion by volume? Explain.

Ans: According to the laws of proportion of volume the volume of the reactant and the product will be the same as this given by the scientific research of Gay-Lussac. 

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