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NCERT Exemplar Class 10 Science Solutions Chapter 1 Chemical Reactions and Equations

NCERT Exemplar Class 10 Science Solutions Chapter 1 Chemical Reactions and Equations

Edited By Shivani Poonia | Updated on Jun 09, 2025 12:53 PM IST

The NCERT Exemplar Class 10 Science Chapter 1 presents systematic explanations of chemical reactions and equations that form the basis of chemistry-based transformations, undergoing various chemical changes. The chapter covers easy-to-complex reactions and their practical applications in the real world. These solutions for Class 10 Science Chapter 1 are important and are often asked in exam,s covering a good percentage of marks. The questions on this topic are mostly practice-based and will help you in understanding concepts more precisely.

This Story also Contains
  1. NCERT Exemplar Class 10 Science Solutions Chapter 1- MCQ
  2. NCERT Exemplar Class 10 Science Solutions Chapter 1-Short Answer
  3. NCERT Exemplar Class 10 Science Solutions Chapter 1-Long Answer
  4. Important Question From NCERT Exemplar Class 10 Science Chapter 1
  5. Approach To Solve Class 10 Science Chapter 1 Questions
  6. NCERT Exemplar Class 10 Science Chapter 1 Topic And Subtopics:
  7. NCERT Class 10 Science Exemplar Solutions for Other Chapters
  8. NCERT Solutions for Class 10 Science Chapter-wise
  9. NCERT books and syllabus
NCERT Exemplar Class 10 Science Solutions Chapter 1 Chemical Reactions and Equations
NCERT Exemplar Class 10 Science Solutions Chapter 1 Chemical Reactions and Equations

Our subject experts have provided the solutions with easy-to-follow step-by-step explanations so that the students can build strong conceptual knowledge. The NCERT exemplar solutions follow the CBSE 2025 syllabus to properly train students for their board exams and their performances in competitive examinations.

These NCERT Exemplar solutions of class 10 will help the students to build a deeper understanding of the topics covered. The complete set of solutions serves as a tool to improve practice and problem-solving abilities and to deliver improved academic performance. Students who use these resources feel more confident in science classes and achieve better grades.

Let us look into some of the questions and their solutions to get a proper understanding of the chapter.

NCERT Exemplar Class 10 Science Solutions Chapter 1- MCQ

Question:1

Which of the following is not a physical change?
(a) Boiling of water to give water vapour
(b) Melting of ice to give water
(c) Dissolution of salt in water
(d) Combustion of Liquefied Petroleum Gas (LPG)

Answer: (d)

(a) Boiling of water to give water vapour – Change in state – Physical change
(b) Melting of ice to give water - Change in state – Physical change
(c) Dissolution of salt in water - When salt is mixed with water, the salt dissolves because the covalent bonds of water are stronger than the ionic bonds in the salt molecules. This is considered as a physical change.
(d) LPG is liquefied petroleum gas, which reacts with oxygen to form new products as carbon dioxide (CO2) and water (H2O). Therefore, combustion of LPG is a chemical change.
Combustion is always a chemical change because it is irreversible.

Question:2

The following reaction is an example of a:
4NH3(g)+5O2(g)4NO(g)+6H2O(g)
(i) displacement reaction
(ii) combination reaction
(iii) redox reaction
(iv) neutralisation reaction
(a) (i) and (iv) (b) (ii) and (iii)
(c) (i) and (iii) (d) (iii) and (iv)

Answer: (c)

4NH3(g)+5O2(g)4NO(g)+6H2O(g)
Oxygen displaces hydrogen of ammonia. Hence, this is a displacement reaction. Nitrogen of ammonia is getting oxidized with the addition of oxygen. This is an example of redox reaction.
Hence it is an example of displacement as well as redox reaction.

Question:3

Which of the following statements about the given reaction are correct?
3Fe(s)+4H2O(g)Fe3O4(s)+4H2(g)
(i) Iron metal is getting oxidised
(ii) Water is getting reduced
(iii) Water is acting as reducing agent
(iv) Water is acting as oxidising agent
(a) (i), (ii) and (iii) (b) (iii) and (iv)
(c) (i), (ii) and (iv) (d) (ii) and (iv)

Answer: (c)

3Fe(s)+4H2O(g)Fe3O4(s)+4H2(g)
Oxygen combines with water to get oxidized.
Oxygen is removed from water hence it is getting reduced.
Water is providing oxygen and it acts as an oxidizing agent.

Question:4

Which of the following are exothermic processes?
(i) Reaction of water with quick lime
(ii) Dilution of an acid
(iii) Evaporation of water
(iv) Sublimation of camphor (crystals)
(a) (i) and (ii) (b) (ii) and (iii)
(c) (i) and (iv) (d) (iii) and (iv)

Answer: (a)

When water reacts with water and acid it releases enormous amount of heat. Similarly, when water reacts with quick lime it releases a lot of heat.
When water reacts with quick lime, calcium hydroxide is formed along with release of heat. Hence, it is an exothermic reaction.
Dilution of an acid – Highly exothermic
Evaporation of water and sublimation of camphor are examples of endothermic reactions.

Question:5

Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in case of beaker C, the temperature of the solution falls. Which one of the following statement(s) is(are) correct?
(i) In beakers A and B, exothermic process has occurred.
(ii) In beakers A and B, endothermic process has occurred.
(iii) In beaker C exothermic process has occurred.
(iv) In beaker C endothermic process has occurred.
(a) (i) only (b) (ii) only
(c) (i) and (iv) (d) (ii) and (iii)

Answer: (c)

In beaker A:
NaOH+H2ONa++OH+H2O+heat
In beaker B:
CuSO4(s)+5H2O(l)CuSO4.5H2O(s)
Both are exothermic processes. These will increase the temperature
In beaker C:
NaCl+H2O+heatNa++Cl+H2O
This is an endothermic process and this will decrease the temperature.

Question:6

A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?
(a) KMnO4 is an oxidising agent, it oxidises FeSO4
(b)FeSO4 acts as an oxidising agent and oxidises KMnO4
(c) The colour disappears due to dilution; no reaction is involved
(d) KMnO4 is an unstable compound and decomposes in presence of FeSO4 to a colourless compound.

Answer: (a)

FeSO4+KMnO4+H2SO4Fe2(SO4)3+MnSO4+K2SO4+H2O
KMnO4 acts as an oxidizing agent, it oxidizes FeSO4(Fe+2)toFe2(SO4)3(Fe+3)

Question:7

Which among the following is(are) double displacement reaction(s)?
(i) Pb+CuCl2PbCl2+Cu
(ii) Na2SO4+BaCl2BaSO4+2NaCl
(iii) C+O2CO2
(iv) CH4+2O2CO2+2H2O
(a) (i) and (iv) (b) (ii) only
(c) (i) and (ii) (d) (iii) and (iv)

Answer: (b)

Double displacement reactions are those in which ions of the reactants are exchanged to form new compounds as products.
Na+ ion combines with Cl ion and SO42 ion combines with Ba2+ ion to form two new compounds as sodium chloride (NaCl) and barium sulphate (BaSO4)respectively.
Sodium and Barium are displaced from each other’s salts hence it is a double displacement reaction.

Question:8

Which among the following statement(s) is(are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to:
(i) the formation of silver by decomposition of silver chloride
(ii) sublimation of silver chloride
(iii) decomposition of chlorine gas from silver chloride
(iv) oxidation of silver chloride
(a) (i) only (b) (i) and (iii)
(c) (ii) and (iii) (d) (iv) only

Answer: (a)

2AgCllight2Ag+Cl2
Exposure of silver chloride to sunlight for a long duration yields silver metal and chlorine gas.
The white color of silver chloride changes to grey due to the formation of silver metal.

Question:9

Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?
(i) It is an endothermic reaction
(ii) It is an exothermic reaction
(iii) The pH of the resulting solution will be more than seven
(iv) The pH of the resulting solution will be less than seven
(a) (i) and (ii) (b) (ii) and (iii)
(c) (i) and (iv) (d) (iii) and (iv)

Answer:(b)

CaO+H2OCa(OH)2+heat
When solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. It proves the reaction is exothermic.
pH of the solution will be more than 7 because oxides and hydroxides of metals are alkaline.

Question:10

Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?
(i) Displacement reaction
(ii) Precipitation reaction
(iii) Combination reaction
(iv) Double displacement reaction
(a) (i) only (b) (ii) only
(c) (iv) only (d) (ii) and (iv)

Answer: (d)

BaCl2+(NH4)2SO4BaSO4+2NH4Cl
Ammonium and barium are getting displaced from their respective salts.
This reaction is an example of double displacement reaction as ions (both cations and anions) of the reacting molecules are exchanged.
Barium ion (Ba2+) combines with sulphate ion (SO42) to form Barium sulphate (BaSO4) and ammonium ion (NH4+) combines with chloride ion (Cl) ion to form ammonium chloride (NH4Cl).
The above reaction is also a precipitation reaction because barium and sulphate ions combine to form precipitates of barium sulphate.

Question:11

Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is:
(a) 1:1
(b) 2:1
(c) 4:1
(d) 1:2

Answer:(b)

The reaction is shown as:
2H2O(l)2H2(g)+O2(g)
1 Mole of water has 2 moles of Hydrogen and 1 mole of water.
Therefore, the mole ratio of hydrogen and oxygen gas liberated is 2:1.

Question:12

Which of the following is(are) an endothermic process(es)?
(i) Dilution of sulphuric acid
(ii) Sublimation of dry ice
(iii) Condensation of water vapours
(iv) Evaporation of water
(a) (i) and (iii) (b) (ii) only
(c) (iii) only (d) (ii) and (iv)

Answer: (d)

Dilution of sulphuric acid with water is a highly exothermic process as it occurs with the evolution of heat.
Sublimation of ice is a direct phase transition from solid to gas
Condensation is the change of water from its gaseous form (water vapor) into liquid water.
Evaporation is the process by which water changes from a liquid to a gas or vapor.
Change of solid to gas or liquid to gas absorbs heat hence it is an endothermic reaction.

Question:13

In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?
(a) Lead sulphate (insoluble)
(b) Lead acetate
(c) Ammonium nitrate
(d) Potassium sulphate

Answer: (b)

2KI(aq)+Pb(NO3)2(aq)PbI2(s)+2KNO3
Potassium Iodide(KI) and lead nitrate Pb(NO3)2 dissociate in their aqueous states to form ions.
Precipitates of lead iodide (PbI2) are formed.
Lead sulphate being insoluble in water does not give Pb2+ ions which can combine with I to form (PbI2)

Question:14

Which of the following gases can be used for storage of fresh sample of an oil for a long time?
(a) Carbon dioxide or oxygen
(b) Nitrogen or oxygen
(c) Carbon dioxide or helium
(d) Helium or nitrogen

Answer: (d)

Helium can be used as it is an inert gas. Nitrogen is less reactive and it is cheaper than Helium.
Hence Helium, just as nitrogen, can be used for storage of a fresh sample of an oil for quite a while on the grounds that they avoid the oil from rancidity.
The contact of air and oil is forestalled by utilizing nitrogen or helium as covering gas.

Question:15

The following reaction is used for the preparation of oxygen gas in the laboratory
2KClO3(s)catalystheat2KCl(s)+3O2(g)
Which of the following statement(s) is(are) correct about the reaction?
(a) It is a decomposition reaction and endothermic in nature
(b) It is a combination reaction
(c) It is a decomposition reaction and accompanied by release of heat
(d) It is a photochemical decomposition reaction and exothermic in nature

Answer: (a)

Potassium chlorate decomposes to give potassium chloride and oxygen. This is a decomposition reaction
Also as shown in the equation, heat is supplied for the reaction to take place. Hence it is endothermic in nature.

Question:16

Which one of the following processes involve chemical reactions?
(a) Storing of oxygen gas under pressure in a gas cylinder
(b) Liquefaction of air
(c) Keeping petrol in a china dish in the open
(d) Heating copper wire in presence of air at high temperature

Answer: (d)

Storing of oxygen gas under pressure in a gas cylinder – does not involve chemical reactions
Liquefaction of air - Air is liquefied by the Linde process, in which air is alternately compressed, cooled, and expanded, each expansion results in a considerable reduction in temperature. With the lower temperature the molecules move more slowly and occupy less space, so the air changes phase to become liquid. Hence it does not involve chemical reactions
Keeping petrol in a china dish in the open – does not involve chemical reactions
When copper is heated in the presence of air in a very high temperature, a chemical reaction takes place.
2Cu+O22CuO

Question:17

In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature?
(a) 2H2(l)+O2(l)2H2O(g)
(b) 2H2(g)+O2(l)2H2O(l)
(c) 2H2(g)+O2(g)2H2O(l)
(d) 2H2(g)+O2(g)2H2O(g)

Answer: (c)

At room temperature hydrogen and oxygen are gases while water is liquid in nature hence option (c) represents correct states of reactants and products.

Question:18

Which of the following are combination reactions?
(i)2KClO3heat2KCl+3O2
(ii)MgO+H2OMg(OH)2
(iii) 4Al+3O22Al2O3
(iv) Zn+FeSO4ZnSO4+Fe
(a) (i) and (iii) (b) (iii) and (iv)
(c) (ii) and (iv) (d) (ii) and (iii)

Answer:

Ans. (d)
A combination reaction is a reaction where two or more elements or compounds combine to form a single compound.
(i) )2KClO3heat2KCl+3O2
Decomposition reaction.
(ii)MgO+H2OMg(OH)2
Combination reaction as magnesium oxide and water combine to form magnesium hydroxide
(iii) 4Al+3O22Al2O3
Combination reaction as aluminium combines with oxygen to form aluminium oxide
(iv)Zn+FeSO4ZnSO4+Fe
Displacement reaction.

Question:19

Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas.
(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H2SO4.
(d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.

Answer:

Chemical Reactions and Equations
(aN2(g)+3H2(g)2NH3(g)
Combination reaction.
(b)NaOH(aq)+CH3COOH(l)CH3COONa(aq)+H2O(l)
Neutralisation reaction between a strong base and weak acid
(c)C2H5OH(aq)+CH3COOH(l)CH3COOC2H5(aq)+H2O(l)
Double displacement reaction.
(d) C2H4(g)+3O2(g)2CO2(g)+2H2O(g)+Heat+Light
Oxidation reaction.

Question:20

Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Thermit reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat.

Answer:

(a) Thermit reaction, iron (III) oxide reacts with aluminum and gives molten iron and aluminum oxide.
Fe2O3+2AlAl2O3(s)+2Fe+heat
Single displacement reaction
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
3Mg(s)+N2Mg3N2
Combination reaction
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
Cl2(g)+2KI(aq)2KCl(aq)+I2(s)
Displacement reaction
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat.
C2H5OH+3O22CO2+3H2O+heat
Combustion reaction

Question:21

Complete the missing components/variables given as x and y in the following reactions
(a) Pb(NO3)2(aq)+2KI(aq)PbI2(x)+2KNO3(y)
(b) Cu(s)+2AgNO3(aq)Cu(NO3)2(aq)+x(s)
(c) Zn(s)+H2SO4(aq)ZnSO4(x)+H2(y)
(d) CaCO3(s)xCaO(s)+CO2(g)

Answer:

a) x (s), y (aq)
Pb(NO3)2(aq)+2KI(aq)PbI2(s)+2KNO3(aq)
b) x is 2Ag
Cu(s)+2AgNO3(aq)Cu(NO3)2(aq)+2Ag(s)
c) x (aq), y(g)
Zn(s)+H2SO4(aq)ZnSO4(aq)+H2(g)
d) x is heat
CaCO3(s)heatCaO(s)+CO2(g)

Question:22

Which among the following changes are exothermic or endothermic in nature?
(a) Decomposition of ferrous sulphate
(b) Dilution of sulphuric acid
(c) Dissolution of sodium hydroxide in water
(d) Dissolution of ammonium chloride in water

Answer:

(a) Decomposition of ferrous sulphate
2FeSO4(s)heatFe2O3(s)+SO3(g)+SO2(g)
Endothermic reaction as it involves absorption of heat
(b) Dilution of sulphuric acid
Dilution of sulphuric acid with water is a highly exothermic process as it occurs with the evolution of heat.
H2SO4+2H2O2H3O++SO42+Heat
Exothermic reactions
(c) Dissolution of sodium hydroxide in water
It produces negative hydroxide ions and positive sodium ions (Na+)
NaOHwaterNa++OH+Heat
Exothermic reactions
(d) Dissolution of ammonium chloride in water
NH4Cl(s)NH4+(aq)+Cl(aq)
Endothermic reaction

Question:23

Identify the reducing agent in the following reactions
(a) 4NH3+5O24NO+6H2O
(b) H2O+F2HF+HOF
(c) Fe2O3+3CO2Fe+3CO2
(d) 2H2+O22H2O

Answer:

Reducing agent is the one which reduces other substance (by removal of oxygen or addition of hydrogen) and itself gets oxidised.
In the given reactions, reducing agents are as follows:
a) NH3 - Ammonia
b) F2 - Fluorine
c) CO - Carbon monoxide
d) H2 - Hydrogen

Question:24

Identify the oxidising agent (oxidant) in the following reactions
(a) Pb3O4+8HCl3PbCl2+Cl2+4H2O
(b) 2Mg+O22MgO
(c) CuSO4+ZnCu+ZnSO4
(d) V2O5+5Ca2V+5CaO
(e) 3Fe+4H2OFe3O4+4H2
(f) CuO+H2Cu+H2O

Answer:

An oxidizing agent is a reactant that removes electrons from other reactants during a redox reaction. The oxidizing agent typically takes these electrons for itself, thus gaining electrons and being reduced.
In the above reactions, oxidizing agents are:
a) Pb3O4
b) O2
c) CuSO4
d) V2O5
e) H2O
f) CuO

Question:25

Write the balanced chemical equations for the following reactions
(a) Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogencarbonate.
(b) Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.
(c) Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (Cu2I2), liberates iodine gas and also forms potassium sulphate.

Answer:

(a) Na2CO3+HClNaCl+NaHCO3
(b) NaHCO3+HClNaCl+H2O+CO2
(c) 2CuSO4+4KI2K2SO4+Cu2I2+I2

Question:26

A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction?

Answer:

KCl(aq)+AgNO3(aq)AgCl(s)+KNO3(aq)
This is a double displacement (both reactants exchange ions to form new products) and precipitation reaction (white precipitate of silver chloride (AgCl) is formed).

Question:27

Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.

Answer:

2FeSO4(s)heatFe2O3(s)+SO2(g)+SO3(g)
This is a decomposition reaction.
Ferrous sulphate decomposes on heating to ferric oxide.

Question:28

Why do fire flies glow at night?

Answer:

Fire flies produces an enzyme called as luciferase which carries oxidation of Magnesium Because of oxidation of Magnesium in presence of atmospheric oxygen fire flies’ glows in the night. This phenomenon of glowing by living organisms is called bioluminescence.

Question:29

Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

Answer:

Grapes on the plant do not ferment because of defense mechanism of plants. When grapes are plucked from plant, grapes reacts with yeast to carry out fermentation. Here sugar changes to alcohol and it is a chemical change.

Question:30

Which among the following are physical or chemical changes?
(a) Evaporation of petrol
(b) Burning of Liquefied Petroleum Gas (LPG)
(c) Heating of an iron rod to red hot.
(d) Curdling of milk
(e) Sublimation of solid ammonium chloride

Answer:

Physical changes only change the appearance of a substance, not its chemical composition.
Chemical changes cause a substance to change into an entirely substance with a new chemical formula.
Physical changes
(a) Evaporation of petrol
(b) Heating of an iron rod to red hot.
(e) Sublimation of solid ammonium chloride
Chemical changes
(c) Burning of Liquefied Petroleum Gas (LPG)
(d) Curdling of milk

NCERT Exemplar Class 10 Science Solutions Chapter 1-Short Answer

Question:31

During the reaction of some metals with dilute hydrochloric acid, following observations were made.
(a) Silver metal does not show any change
(b) The temperature of the reaction mixture rises when aluminium(Al) is added.
(c) The reaction of sodium metal is found to be highly explosive
(d) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
Explain these observations giving suitable reasons.

Answer:

a) There will not be any reaction between silver and dilute HCl as silver lies in low reactive series of metals.
b) When aluminium is added, it is an exothermic reaction and temperature increase
c) Sodium is highly reactive metal. It reacts with atmospheric oxygen to form exothermic reaction which result in temperature increase.
d) When lead reacts with acid it produces hydrogen gas which are responsible for the formation of bubbles.

Question:32

A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved

Answer:

Compound X is Calcium oxide.
CaO is extensively used in cement industry. On treatment with water, CaO produces Ca(OH)2 which is alkaline in nature and turns red litmus to blue color.
CaO(s)+H2O(l)Ca(OH)2(aq)

Question:33

Write a balanced chemical equation for each of the following reactions and also classify them.
(a) Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
(b) A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.
(c) Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
(d) Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water.

Answer:

(a) Pb(CH3COO)2+2HClPbCl2+CH3COOH
This is a Double Displacement reaction.
(b) 2Na+2C2H5OH2C2H5ONa++H2
This is a Displacement reaction.
(c) Fe2O3+3CO2Fe+3CO2
This is a redox reaction.
(d) 2H2S+O22S+2H2O
This is a redox reaction.

Question:34

Why do we store silver chloride in dark coloured bottles?

Answer:

Silver chloride decomposes into silver and chlorine gas when exposed to sunlight.
2AgCl2Ag+Cl2?
Hence Silver chloride is stored in dark colored bottles.

Question:35

Balance the following chemical equations and identify the type of chemical reaction.
(a) Mg(s)+Cl2(g)MgCl2(s)
(b) HgO(s)Hg(l)+O2(g)
(c) Na(s)+S(s)Na2S(s)
(d) TiCl4(l)+Mg(s)Ti(s)+MgCl2(s)
(e) CaO(s)+SiO2(s)CaSiO3(s)
(f) H2O2(l)H2O(l)+O2(g)

Answer:

(a)Mg(s)+Cl2(g)MgCl2(s)
This type of reaction is called a combination reaction or a synthesis reaction.
(b) 2HgO(s)heat2Hg(l)+O2(g)
This is an example of thermal decomposition reaction.
(c) 2Na(s)+S(s)Na2S(s)
This is an example of a Combination reaction.
(d) TiCl4(l)+Mg(s)Ti(s)+2MgCl2(s)
This reaction falls under the category of Displacement reactions
(e) CaO(s)+SiO2(s)UVCaSiO3(s)
This is a synthesis reaction.
(f) 2H2O2(l)2H2O(l)+O2(g)
This is a decomposition reaction.

Question:36

A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.
(a) Write the chemical formulae of X and Y.
(b) Write a balanced chemical equation, when X is dissolved in water.

Answer:

(a) 2Mg+O22MgO
Compound X: MgO [Magnesium Oxide]
Compound Y: Mg3N2 [Magnesium Nitride]
(b) If Magnesium Oxide is dissolved in water, the product is Magnesium Hydroxide
MgO+H2OMg(OH)2

Question:37

Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why?

Answer:

Zinc is more reactive than copper as Zinc is placed above Hydrogen and Copper is placed below hydrogen in the activity series of metals. Because of this Zinc reacts with HCl whereas Copper will not react.
Zn>Fe>Pb>H>Cu>Hg
Zn+2HCl(dil)ZnCl2+H2?

Question:38

A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.
(a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
(b) Name the black substance formed and give its chemical formula.

Answer:

a) Silver reacts with H2S present in the atmosphere to form a black color compound Silver Sulphide. This phenomenon is called as corrosion.
b) Black color compound formed is Silver Sulphide
2Ag+H2SAg2S+H2

Question:39

On heating blue coloured powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed
(a) Write a balanced chemical equation of the reaction.
(b) Identity the brown gas X evolved.
(c) Identity the type of reaction.
(d) What could be the pH range of aqueous solution of the gas X?

Answer:

Blue coloured powder of copper (II) nitrate = Cu(NO3)2
(a) 2Cu(NO3)22CuO+4NO2+O2
(b) The brown gas X is nitrogen dioxide, NO2
(c) Reaction involved is Thermal decomposition.
(d) pH< 7 because NO2 dissolves in water to form acidic solution (pH range below 7).

Question:40

Give the characteristic tests for the following gases
(a) CO2
(b) SO2
(c) O2
(d) H2

Answer:

(a) Pass CO2 into limewater which will turn limewater milky. This is the confirmation test for the presence of carbon-dioxide.
Ca(OH)2(aq)+CO2CaCO3(Whitecolor)+H2O
(b) 1) Smell is the characteristic feature of SO2 which smells like rotten egg.
2) Sulphur dioxide gas turns moist litmus paper from blur to red as sulphur dioxide is acidic in nature.
3) Sulphur dioxide gas turns acidified potassium dichromate solution from orange to green (Conformation Test)
(c) Test for oxygen involves burning of match stick near oxygen. It makes the match stick burn even more brightly.
(d) When burning matchstick is brought near H2 gas, the flame burns with the pop sound. This is the test to confirm Hydrogen gas.

Question:41

What happens when a piece of
(a) zinc metal is added to copper sulphate solution?
(b) aluminium metal is added to dilute hydrochloric acid?
(c) silver metal is added to copper sulphate solution?
Also, write the balanced chemical equation if the reaction occurs

Answer:

(a) When Zinc is added to copper sulphate solution Zinc displaces copper to form Zinc sulphate.
Zn(s)+CuSO4(aq)ZnSO4(aq)+Cu(s)
(b) Aluminium metal reacts with dilute HCl to for Aluminum Chloride and Hydrogen gas is evolved in the reaction.
2Al(s)+6HCl(aq)2AlCl3(aq)+3H2
(c) When silver metal is added to Copper Sulphate solution there will not be any reaction as silver is non-reactive metal.

NCERT Exemplar Class 10 Science Solutions Chapter 1-Long Answer

Question:43

On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, white precipitate is obtained.
(a) Write a balanced chemical equation of the reaction involved
(b) What other name can be given to this precipitation reaction?
(c) On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why?

Answer:

(a) On adding a drop of Barium Chloride solution to an aqueous solution of sodium sulphite, barium sulphite is obtained which is white color precipitate.
BaCl2+Na2SO3BaSO3+2NaCl
(b) In this case precipitation reaction is a double displacement.
(c) When we add dilute HCl to this reaction mixture Barium chloride, Sulphur dioxide and water are formed. Barium chloride is a soluble substance which will make the white precipitate disappear.
BaSO3+2HClBaCl2+SO2+H2O.

Question:44

You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO3,ZnCl2andH2O. In which of the above containers these solutions can be kept?

Answer:

Dilute HCl
Copper does not react with dilute HCl, so it can be stored in a copper vessel
Dilute HNO3
3Cu(s)+8HNO3(aq)3Cu(NO3)2(aq)+2NO(g)+4H2O(l)
Cannot be stored in copper vessel as above chemical reaction takes place.
Hence stored in aluminium vessel
ZnCl2
No reaction takes place because copper is less active metal than zinc and can't displace it from ZnCl2 solution.
Hence stored in copper vessel
H2O
No reaction occurs between copper and water so water can be stored in copper vessel.

Important Question From NCERT Exemplar Class 10 Science Chapter 1

Question:

A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?

(a) KMnO4 is an oxidising agent, it oxidises FeSO4

(b) FeSO4 acts as an oxidising agent and oxidises KMnO4

(c) The colour disappears due to dilution; no reaction is involved

(d) KMnO4 is an unstable compound and decomposes in the presence of FeSO4 to a colorless compound.

Answer-

The purple color of the solution was due to potassium permanganate, which acts as an oxidizing agent. When it oxidises FeSO4 the purple colour fades away

Hence, the correct option is option (a).

Approach To Solve Class 10 Science Chapter 1 Questions

1. Revise The Basics

Recall the fundamentals before diving into question solving practice.

  • Chemical reaction is defined as the process where reactants is converted into products (e.g., Mg+O2MgO ).

  • Balance the equation by keeping the number of atoms of each element on both sides equal.

  • There are different kinds of reaction like

    • Combination: A+BAB

    • Decomposition: ABA+B

    • Displacement: A+BCAC+B

    • Double Displacement: AB+CDAD+CB

    • Redox (Oxidation-Reduction): Identify the species that is oxidized/reduced.

  • Reaction is carried out and marked by color change, gas evolution, temperature change or precipitate formation.

2. Step-by-Step Problem Solution

A.How to write and balance Chemical Equations Example: Write the balanced equation for hydrogen and oxygen forming water.

  • Unbalanced Equation: H2+O2H2O

  • Balance Atoms:

Oxygen is 2 on LHS and 1 on RHS, so multiply H2O by 2

H2+O22H2O

Now, Hydrogen is 4 on RHS and 2 on LHS , so Multiply H2 by 2

2H2+O22H2O (Balanced)

Tip: Balance the metals first, then the nonmetals, and finally hydrogen/oxygen.

3. Practice Tips

  • Memorize the common reactions like photosynthesis, combustion, etc.

  • Use NCERT Examples to focus on in-text and back-exercise questions.

  • Practice the diagrams like experiments (e.g., electrolysis of water).

  • Recheck and verify atom counts after balancing the reaction.

4. Avoid making common mistakes

  • Like forgetting to balance charges in ionic reactions.

  • Not specifying the reaction type correctly

NCERT Exemplar Class 10 Science Chapter 1 Topic And Subtopics:

1.Chemical Equations

  • Writing Chemical Equation

  • Balanced Chemical Equations

2. Types of Chemical Reactions

  • Combination Reaction

  • Decomposition Reaction

  • Displacement Reaction

  • Double Displacement Reaction

  • Oxidation And Reduction

3. Have you observed the effects of oxidation in everyday life

  • Corrosion

  • Rancidity

NCERT Class 10 Science Exemplar Solutions for Other Chapters

Below are the chapters to go through-

NCERT Solutions for Class 10 Science Chapter-wise

The NCERT Solutions for all Class 10 science chapters are given below-

NCERT books and syllabus

Also Read,

Frequently Asked Questions (FAQs)

1. How to balance chemical equations easily?

First, count the atoms of each element on both sides of a chemical equation. Adjust the coefficients to make the number of atoms equal on both sides. Start with the most complex molecule and balance one element at a time.


2. What is the difference between exothermic and endothermic reactions?

An exothermic reaction is a type of reaction in which heat is released, e.g., burning fuel and respiration. On the other hand, an endothermic reaction is one in which heat is absorbed that causes the surroundings to cool down. For example, photosynthesis and melting ice


3. What are some real-life examples of chemical reactions?

Looking around the surroundings, you can find a bunch of examples. Some of them are given below:

1. Rusting of iron - When iron reacts with oxygen and water it forms rust.

2. Cooking food - Heat causes chemical changes in ingredients to form new substances.

3. Digestion - The food we eat breaks down into simpler substances in our body.

4. Why is respiration considered an exothermic reaction?

Respiration is considered an exothermic reaction because it releases energy in the form of heat.  When glucose and oxygen combine during respiration, it produces carbon dioxide, water, and energy. The body uses this energy to stay warm and carry out several tasks.


5. What are the key differences between physical and chemical changes?

A physical change is a reversible change in which no new substance is formed, while a chemical change is an irreversible change where one or more new substances are formed.


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A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg

 

An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)

K/2\,

Option 2)

\; K\;

Option 3)

zero\;

Option 4)

K/4

In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

Option 4)

67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)

0.02

Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)

Molality

Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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