Class 10 Science · Chapter 1

Chemical Reactions and Equations

298 Class 10 Science questions on Chemical Reactions and Equations from the NCERT textbook, NCERT Exemplar and CBSE board papers 2018–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 9 of 15

1. Q161 CBSE 2025
   Define ​a ​precipitation reaction. ​Give its example and also express the reaction ​that ​occurs ​in the form of a balanced chemical equation.
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   A precipitation reaction forms an insoluble solid on mixing solutions, e.g. sodium sulphate and barium chloride give white barium sulphate.

   A precipitation reaction is a reaction in which two solutions are mixed and an insoluble substance, called a precipitate, is formed and separates out as a solid. Example: when sodium sulphate solution is mixed with barium chloride solution, a white precipitate of barium sulphate is formed. ${\text{Na}}_2{\text{SO}}_4(aq)+{\text{BaCl}}_2(aq)\to {\text{BaSO}}_4(s)+2\text{NaCl}(aq)$

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2. Q162 CBSE 2025
   Write ​balanced ​chemical equation for each of the following reactions :

   1. (i)Sodium metal reacts with water to produce ​sodium hydroxide and hydrogen gas.
   2. (ii)Lead nitrate is heated to produce lead oxide, ​nitrogen dioxide ​and oxygen.
   3. (iii)​Nitrogen gas combines with hydrogen to form ammonia.
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   Sodium and water give $\text{NaOH}$ and ${\text{H}}_2$; lead nitrate gives $\text{PbO}$, ${\text{NO}}_2$ and ${\text{O}}_2$; nitrogen and hydrogen combine as ${\text{N}}_2+3{\text{H}}_2\to 2{\text{NH}}_3$.

   (i) $2\text{Na}+2{\text{H}}_2\text{O}⟶2\text{NaOH}+{\text{H}}_2\uparrow$; (ii) $2{\text{Pb(NO}}_3{)}_2\stackrel{\text{heat}}{\to }2\text{PbO}+4{\text{NO}}_2+{\text{O}}_2$; (iii) ${\text{N}}_2+3{\text{H}}_2⟶2{\text{NH}}_3$

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3. Q163 CBSE 2025
   Define a displacement ​reaction. ​Name a displacement reaction which is highly exothermic and ​has its use ​in joining railway tracks. Explain the process with ​a ​balanced chemical ​equation ​of the reaction that occurs.
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   The thermite reaction between aluminium and ferric oxide gives molten iron that welds rail ends; aluminium displaces iron because it is more reactive.

   A displacement reaction is one in which a more reactive element displaces a less reactive element from its compound, $\text{A}+\text{BC}\to \text{AC}+\text{B}$. The highly exothermic displacement reaction used to join railway tracks is the thermite reaction. A mixture of aluminium powder and ferric oxide is taken in a crucible above the gap between the two broken rail ends and ignited with a magnesium ribbon; aluminium, being more reactive than iron, displaces iron from ferric oxide and the reaction releases so much heat that the iron is produced in the molten state. The molten iron runs into the gap and on solidifying welds the rail ends together. ${\text{Fe}}_2{\text{O}}_3(s)+2\text{Al}(s)\to 2\text{Fe}(l)+{\text{Al}}_2{\text{O}}_3(s)+\text{heat}$

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4. Q164 CBSE 2025
   When dry crystals of ferrous sulphate were heated in a dry boiling tube, some tiny water droplets were observed in the tube after some time.

   1. (i)State the source of these water droplets.
   2. (ii)Write the colour ​change observed ​during ​heating.
   3. (iii)Write the balanced chemical equation of the reaction that occurs during heating.
   4. (iv)How many water ​molecules ​are attached per formula unit of ​ferrous sulphate ​crystal ?
   5. (v)Write the molecular formula of crystalline form of (I) copper sulphate, and (II) sodium carbonate.
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   The droplets are water of crystallisation; green crystals turn dirty white, then reddish brown; ${\text{FeSO}}_4\cdot 7{\text{H}}_2\text{O}$ has 7 water molecules.

   (i) The droplets are the water of crystallisation of the ferrous sulphate crystals, ${\text{FeSO}}_4\cdot 7{\text{H}}_2\text{O}$; on heating the crystals lose it as vapour, which condenses on the cooler part of the tube. (ii) The green colour of the crystals fades to dirty white as the water of crystallisation is lost, and on stronger heating a reddish brown residue of ferric oxide is left, with a smell of burning sulphur. (iii) $2{\text{FeSO}}_4\stackrel{\Delta }{\to }{\text{Fe}}_2{\text{O}}_3+{\text{SO}}_2+{\text{SO}}_3$, the loss of water being ${\text{FeSO}}_4\cdot 7{\text{H}}_2\text{O}\to {\text{FeSO}}_4+7{\text{H}}_2\text{O}$. (iv) Seven water molecules are attached per formula unit. (v) (I) Copper sulphate crystals: ${\text{CuSO}}_4\cdot 5{\text{H}}_2\text{O}$; (II) Sodium carbonate crystals: ${\text{Na}}_2{\text{CO}}_3\cdot 10{\text{H}}_2\text{O}$.

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5. Q165 CBSE 2024
   Solid ​Calcium oxide reacts ​vigorously with ​water to form Calcium hydroxide ​accompanied by ​the liberation of heat. From the information ​given above it may ​be concluded that this reaction

   1. (a)is endothermic and pH of the solution formed is more than 7.
   2. (b)is exothermic and pH of the solution formed is 7.
   3. (c)is endothermic and pH of the solution formed is 7.
   4. (d)is exothermic and pH of the solution formed is more than 7.
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   (d) is exothermic and pH of the solution formed is more than 7.

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6. Q166 CBSE 2024
   An ​iron ​nail ​is ​placed in a solution ​of copper sulphate. The ​nail is ​taken out after 15 minutes. The nail will ​be found to be covered with :

   1. (a)blue deposit
   2. (b)brown deposit
   3. (c)grey deposit
   4. (d)green deposit
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   (b) brown deposit

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7. Q167 CBSE 2024
   Identify ​the product ​‘X’ ​obtained in the ​following chemical reaction ​: ${\text{CaCO}}_3\stackrel{\Delta }{\to }\text{‘X’}+{\text{CO}}_2$

   1. (a)Quick lime
   2. (b)Gypsum
   3. (c)Lime Stone
   4. (d)Plaster of Paris
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   (a) Quick lime

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8. Q168 CBSE 2024
   $\text{Zn}+2{\text{CH}}_3\text{COOH}⟶({\text{CH}}_3\text{COO}{)}_2\text{Zn}+{\text{H}}_2$ The above reaction ​is ​a ​:

   1. (a)Decomposition reaction
   2. (b)Displacement reaction
   3. (c)Double displacement reaction
   4. (d)Combination reaction
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   (b) Displacement reaction

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9. Q169 CBSE 2024
   A ​chemical reaction in ​which ​exchange of ​ions ​occurs between the reactants, ​is known ​as ​:

   1. (a)Endothermic Reaction
   2. (b)Exothermic Reaction
   3. (c)Double Displacement Reaction
   4. (d)Displacement Reaction
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   (c) Double Displacement Reaction

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10. Q170 CBSE 2024
    To balance ​the ​following chemical equation, ​the ​values of the coefficients $x$, $y$ ​and $z$ must be respectively ​: $$x\text{Zn}({\text{NO}}_3{)}_2\stackrel{\Delta }{\to }y\text{ZnO}+z{\text{NO}}_2+{\text{O}}_2$$

    1. (a)$4,2,2$
    2. (b)$4,4,2$
    3. (c)$2,2,4$
    4. (d)$2,4,2$
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    (c) $2,2,4$

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11. Q171 CBSE 2024
    Which ​of ​the following is ​not a thermal ​decomposition ​reaction ​?

    1. (a)$2{\text{FeSO}}_4⟶{\text{Fe}}_2{\text{O}}_3+{\text{SO}}_2+{\text{SO}}_3$
    2. (b)${\text{CaCO}}_3⟶\text{CaO}+{\text{CO}}_2$
    3. (c)$2\text{AgCl}⟶2\text{Ag}+{\text{Cl}}_2$
    4. (d)$\text{Pb}({\text{NO}}_3{)}_2⟶2\text{PbO}+4{\text{NO}}_2+{\text{O}}_2$
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    (c) $2\text{AgCl}⟶2\text{Ag}+{\text{Cl}}_2$

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12. Q172 CBSE 2024
    In ​order to ​balance the ​following chemical ​equation, ​the values of $a$, $b$, $c$ ​and $d$ respectively are ​: $$a\text{Pb}({\text{NO}}_3{)}_2\stackrel{\text{heat}}{\to }b\text{PbO}+c{\text{NO}}_2+d{\text{O}}_2$$

    1. (a)2, 4, 2, 1
    2. (b)2, 2, 4, 1
    3. (c)2, 2, 1, 4
    4. (d)2, 2, 3, 4
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    (b) 2, 2, 4, 1

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13. Q173 CBSE 2024
    In the ​following case(s) ​the ​combination reaction ​occurs ​in ​: I. $\text{CuO}+{\text{H}}_2\stackrel{\Delta }{\to }$ II. $\text{ZnO}+\text{C}⟶$ III. $\text{Na}+{\text{O}}_2⟶$ IV. ${\text{CH}}_4+{\text{O}}_2⟶$

    1. (a)Only III
    2. (b)Only IV
    3. (c)II and III
    4. (d)I, III and IV
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    (a) Only III

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14. Q174 CBSE 2024
    When lead ​nitrate ​powder ​is heated in a ​boiling tube, ​three ​substances are produced. These ​three substances are :

    1. (a)$\text{PbO}$, $\text{NO}$ and ${\text{O}}_2$
    2. (b)${\text{PbO}}_2$, $\text{NO}$ and ${\text{NO}}_2$
    3. (c)$\text{PbO}$, ${\text{NO}}_2$ and ${\text{O}}_2$
    4. (d)${\text{PbO}}_2$, ${\text{NO}}_2$ and ${\text{O}}_2$
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    (c) $\text{PbO}$, ${\text{NO}}_2$ and ${\text{O}}_2$

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15. Q175 CBSE 2024
    Select from the following a ​decomposition ​reaction ​in ​which source ​of ​energy for decomposition is ​light :

    1. (a)$2{\text{FeSO}}_4\to {\text{Fe}}_2{\text{O}}_3+{\text{SO}}_2+{\text{SO}}_3$
    2. (b)$2{\text{H}}_2\text{O}\to 2{\text{H}}_2+{\text{O}}_2$
    3. (c)$2\text{AgBr}\to 2\text{Ag}+{\text{Br}}_2$
    4. (d)${\text{CaCO}}_3\to \text{CaO}+{\text{CO}}_2$
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    (c) $2\text{AgBr}\to 2\text{Ag}+{\text{Br}}_2$

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16. Q176 CBSE 2024
    Which ​of ​the ​following is a ​redox reaction, ​but not ​a combination ​reaction ?

    1. (a)$\text{C}+{\text{O}}_2\to {\text{CO}}_2$
    2. (b)$2{\text{H}}_2+{\text{O}}_2\to 2{\text{H}}_2\text{O}$
    3. (c)$2\text{Mg}+{\text{O}}_2\to 2\text{MgO}$
    4. (d)${\text{Fe}}_2{\text{O}}_3+3\text{CO}\to 2\text{Fe}+3{\text{CO}}_2$
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    (d) ${\text{Fe}}_2{\text{O}}_3+3\text{CO}\to 2\text{Fe}+3{\text{CO}}_2$

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17. Q177 CBSE 2024
    Select ​chemical equation of ​a precipitation ​reaction from the ​following :

    1. (a)${\text{Na}}_2{\text{SO}}_4+{\text{BaCl}}_2⟶{\text{BaSO}}_4+2\text{NaCl}$
    2. (b)$2\text{NaOH}+{\text{H}}_2{\text{SO}}_4⟶{\text{Na}}_2{\text{SO}}_4+2{\text{H}}_2\text{O}$
    3. (c)${\text{Fe}}_2{\text{O}}_3+\text{Al}⟶{\text{Al}}_2{\text{O}}_3+2\text{Fe}$
    4. (d)$2{\text{FeSO}}_4\stackrel{\text{heat}}{\to }{\text{Fe}}_2{\text{O}}_3+{\text{SO}}_2+{\text{SO}}_3$
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    (a) ${\text{Na}}_2{\text{SO}}_4+{\text{BaCl}}_2⟶{\text{BaSO}}_4+2\text{NaCl}$

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18. Q178 CBSE 2024
    Select from the following ​a process in which a ​combination reaction ​is ​involved ​:

    1. (a)Black and White photography
    2. (b)Burning of coal
    3. (c)Burning of methane
    4. (d)Digestion of food
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    (b) Burning of coal

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19. Q179 CBSE 2024
    Which ​of the ​following reactions ​is ​an ​endothermic ​reaction ?

    1. (a)Burning of coal
    2. (b)Decomposition of vegetable matter into compost
    3. (c)Process of respiration
    4. (d)Decomposition of calcium carbonate to form quick lime and carbon dioxide.
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    (d) Decomposition of calcium carbonate to form quick lime and carbon dioxide.

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20. Q180 CBSE 2024
    Consider ​the ​following ​Chemical equation : $a{\text{Al}}_2{\text{O}}_3+b\text{HCl}⟶c{\text{AlCl}}_3+d{\text{H}}_2\text{O}$ In order to ​balance this chemical ​equation, the ​values ​of $a$, $b$, $c$ and $d$ must ​be

    1. (a)1, 6, 2 and 3
    2. (b)1, 6, 3 and 2
    3. (c)2, 6, 2 and 3
    4. (d)2, 6, 3 and 2
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    (a) 1, 6, 2 and 3

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