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 12 of 15

1. Q221 CBSE 2023
   The emission of ​brown ​fumes in ​the ​given experimental ​set-up ​is due ​to

   1. (a)thermal decomposition of lead nitrate which produces brown fumes of nitrogen dioxide.
   2. (b)thermal decomposition of lead nitrate which produces brown fumes of lead oxide.
   3. (c)oxidation of lead nitrate forming lead oxide and nitrogen dioxide.
   4. (d)oxidation of lead nitrate forming lead oxide and oxygen.
   Show answer

   (a) thermal decomposition of lead nitrate which produces brown fumes of nitrogen dioxide.

   Step-by-step solution →
2. Q222 CBSE 2023
   When aqueous solutions of ​potassium iodide ​and lead nitrate ​are mixed, ​an insoluble ​substance ​separates out. The chemical equation for the reaction involved is :

   1. (a)$\text{KI}+{\text{PbNO}}_3\to \text{PbI}+{\text{KNO}}_3$
   2. (b)$2\text{KI}+{\text{Pb(NO}}_3{)}_2\to {\text{PbI}}_2+2{\text{KNO}}_3$
   3. (c)$\text{KI}+{\text{Pb(NO}}_3{)}_2\to \text{PbI}+{\text{KNO}}_3$
   4. (d)$\text{KI}+{\text{PbNO}}_3\to {\text{PbI}}_2+{\text{KNO}}_3$
   Show answer

   (b) $2\text{KI}+{\text{Pb(NO}}_3{)}_2\to {\text{PbI}}_2+2{\text{KNO}}_3$

   Step-by-step solution →
3. Q223 CBSE 2023
   The ​balanced chemical equation showing ​reaction between quicklime and ​water is ​:

   1. (a)$2\text{CaO}+{\text{H}}_2\text{O}⟶2\text{CaOH}+{\text{H}}_2+\text{Heat}$
   2. (b)$\text{CaO}+{\text{H}}_2\text{O}⟶{\text{Ca(OH)}}_2+{\text{H}}_2+\text{Heat}$
   3. (c)$\text{CaO}+{\text{H}}_2\text{O}⟶{\text{Ca(OH)}}_2+\text{Heat}$
   4. (d)$2\text{CaO}+3{\text{H}}_2\text{O}⟶2{\text{Ca(OH)}}_3+{\text{O}}_2+\text{Heat}$
   Show answer

   (c) $\text{CaO}+{\text{H}}_2\text{O}⟶{\text{Ca(OH)}}_2+\text{Heat}$

   Step-by-step solution →
4. Q224 CBSE 2023
   Consider ​the following reaction ​: $$4{\text{NH}}_3+5{\text{O}}_2\to 4\text{NO}+6{\text{H}}_2\text{O}$$ This reaction ​is an example of which one of ​the following two reactions ?

   1. (a)Displacement reaction as well as redox reaction
   2. (b)Double displacement reaction as well as redox reaction
   3. (c)Displacement reaction as well as combination reaction
   4. (d)Combination reaction as well as double displacement reaction
   Show answer

   (a) Displacement reaction as well as redox reaction

   Step-by-step solution →
5. Q225 CBSE 2023
   ${\text{MnO}}_2+x\text{HCl}\to {\text{MnCl}}_2+y{\text{H}}_2\text{O}+z{\text{Cl}}_2$ In order ​to ​balance ​the above chemical equation, the values of $x$, $y$ ​and $z$ ​respectively are ​:

   1. (a)$6,2,2$
   2. (b)$4,1,2$
   3. (c)$4,2,1$
   4. (d)$2,2,1$
   Show answer

   (c) $4,2,1$

   Step-by-step solution →
6. Q226 CBSE 2023
   In order to ​balance the ​following chemical equation, ​the values of the ​coefficients $x$ and $y$ ​respectively are ​: $$x{\text{Pb(NO}}_3{)}_2\stackrel{\text{Heat}}{\to }2\text{PbO}+y{\text{NO}}_2+{\text{O}}_2$$

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

   (a) $2,4$

   Step-by-step solution →
7. Q227 CBSE 2023
   A metal ribbon ​'X' burns in oxygen with ​a dazzling white flame forming a white ash 'Y'. ​The ​correct description of ​X, Y and the ​type of ​reaction is ​:

   1. (a)$X=\text{Ca}$ ; $Y=\text{CaO}$ ; Type of reaction = Decomposition
   2. (b)$X=\text{Mg}$ ; $Y=\text{MgO}$ ; Type of reaction = Combination
   3. (c)$X=\text{Al}$ ; $Y={\text{Al}}_2{\text{O}}_3$ ; Type of reaction = Thermal decomposition
   4. (d)$X=\text{Zn}$ ; $Y=\text{ZnO}$ ; Type of reaction = Endothermic
   Show answer

   (b) $X=\text{Mg}$ ; $Y=\text{MgO}$ ; Type of reaction = Combination

   Step-by-step solution →
8. Q228 CBSE 2023
   Study the ​following ​chemical reaction : $2\text{Na}(s)+2{\text{H}}_2\text{O}(l)⟶2\text{NaOH}(aq)+{\text{H}}_2(g)\uparrow$ The ​reducing agent ​in ​this reaction ​is :

   1. (a)$\text{Na}$
   2. (b)${\text{H}}_2\text{O}$
   3. (c)$\text{NaOH}$
   4. (d)${\text{H}}_2$
   Show answer

   (a) $\text{Na}$

   Step-by-step solution →
9. Q229 CBSE 2023
   Select ​the appropriate state symbols of the products given as X and Y in the following chemical equation ​by choosing the ​correct option ​from table given below : $${\text{Zn}}_{(s)}+{\text{H}}_2{\text{SO}}_{4(l)}⟶{\text{ZnSO}}_{4(X)}+{\text{H}}_{2(Y)}$$

   State symbols offered for the two products

   Option	(X)	(Y)
   (a)	(s)	(l)
   (b)	(aq)	(g)
   (c)	(aq)	(s)
   (d)	(g)	(aq)

   1. (a)X is (s) and Y is $(l)$
   2. (b)X is (aq) and Y is (g)
   3. (c)X is (aq) and Y is (s)
   4. (d)X is (g) and Y is (aq)
   Show answer

   (b) X is (aq) and Y is (g)

   Step-by-step solution →
10. Q230 CBSE 2023
    Select endothermic ​reaction ​from ​the ​following :

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

    (b) Decomposition of calcium carbonate to form quick lime and carbon dioxide.

    Step-by-step solution →
11. Q231 CBSE 2023
    Consider the following chemical ​equation I and II I. $\text{Mg}+2\text{HCl}⟶{\text{MgCl}}_2+{\text{H}}_2$ II. $\text{NaOH}+\text{HCl}⟶\text{NaCl}+{\text{H}}_2\text{O}$ The ​correct statement ​about these equations ​is –

    1. (a)'I' is a displacement reaction and 'II' is a decomposition reaction.
    2. (b)'I' is a displacement reaction and 'II' is double displacement reaction.
    3. (c)Both 'I' and 'II' are displacement reactions.
    4. (d)Both 'I' and 'II' are double-displacement reactions.
    Show answer

    (b) 'I' is a displacement reaction and 'II' is double displacement reaction.

    Step-by-step solution →
12. Q232 CBSE 2023
    These ​consist of two ​statements – ​Assertion (A) and Reason (R). ​Answer ​this question selecting ​the ​appropriate option given below.

    Assertion (A): Reaction of Quicklime with water is an exothermic reaction.

    Reason (R): Quicklime reacts vigorously with water releasing a large amount of heat.

    1. (a)Both (A) and (R) are true and (R) is the correct explanation of (A).
    2. (b)Both (A) and (R) are true but (R) is not the correct explanation of (A).
    3. (c)(A) is true but (R) is false.
    4. (d)(A) is false but (R) is true.
    Show answer

    (a) Both (A) and (R) are true and (R) is the correct explanation of (A).

    Step-by-step solution →
13. Q233 CBSE 2023
    Two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to this question ​from the ​codes (a), ​(b), (c) and ​(d) ​as given ​below :

    Assertion (A): In the following reaction $\text{ZnO}+\text{C}⟶\text{Zn}+\text{CO}$, ZnO undergoes reduction.

    Reason (R): Carbon is a reducing agent that reduces ZnO to Zn.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

    Step-by-step solution →
14. Q234 CBSE 2023
    Two statements ​are given — ​one labelled as ​Assertion (A) and the other labelled as ​Reason (R). Select the correct answer to this ​question from the ​codes (a), (b), (c) ​and (d) as given below.

    Assertion (A): In the reaction, ${\text{Na}}_2{\text{SO}}_4+{\text{BaCl}}_2\to {\text{BaSO}}_4+2\text{NaCl}$, sodium chloride is precipitated.

    Reason (R): When an aqueous solution is added to another aqueous solution, an insoluble substance is formed, which is called precipitate.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (d) Assertion (A) is false, but Reason (R) is true.

    Step-by-step solution →
15. Q235 CBSE 2023
    Two statements are given — one labelled as ​Assertion (A) ​and ​the other labelled ​as Reason ​(R). ​Select the correct answer to ​this question from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): ${\text{MnO}}_2+4\text{HCl}⟶{\text{MnCl}}_2+2{\text{H}}_2\text{O}+{\text{Cl}}_2$ is a redox reaction.

    Reason (R): In this reaction, $\text{HCl}$ is oxidised to ${\text{Cl}}_2$ and ${\text{MnO}}_2$ is reduced to ${\text{MnCl}}_2$.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer

    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

    Step-by-step solution →
16. Q236 CBSE 2023
    State ​whether the given chemical reaction is a redox ​reaction or not. Justify your answer. $${\text{MnO}}_2+4\text{HCl}⟶{\text{MnCl}}_2+2{\text{H}}_2\text{O}+{\text{Cl}}_2$$
    Show answer

    Yes, it is a redox reaction: ${\text{MnO}}_2$ is reduced to ${\text{MnCl}}_2$ and $\text{HCl}$ is oxidised to ${\text{Cl}}_2$.

    Yes, it is a redox reaction. ${\text{MnO}}_2$ loses oxygen, so it is reduced to ${\text{MnCl}}_2$ (manganese goes from $+4$ to $+2$). $\text{HCl}$ loses hydrogen (the hydrogen combines with that oxygen to form water), so it is oxidised to ${\text{Cl}}_2$ (chlorine goes from $-1$ to $0$). Since oxidation and reduction occur together in the same change, the reaction is a redox reaction.

    Step-by-step solution →
17. Q237 CBSE 2023
    A metal nitrate 'A' on ​heating ​gives a metal oxide along with evolution of a brown coloured gas 'B' and a colourless gas, which helps in burning. Aqueous solution ​of 'A' when reacted with potassium ​iodide forms a yellow precipitate.

    1. (a)​Identify ​'A' and 'B'
    2. (b)Name the types of both the reactions ​involved in ​the above statement.
    Show answer

    A is lead nitrate and B is nitrogen dioxide; heating is thermal decomposition and the reaction with KI is double displacement (precipitation).

    (a) 'A' is lead nitrate, ${\text{Pb(NO}}_3{)}_2$, and 'B' is nitrogen dioxide, ${\text{NO}}_2$ (the colourless gas that helps burning is oxygen). (b) Heating 'A' is a thermal decomposition reaction: $2{\text{Pb(NO}}_3{)}_2\stackrel{\text{heat}}{\to }2\text{PbO}+4{\text{NO}}_2+{\text{O}}_2$. The reaction with potassium iodide is a double displacement reaction, also called a precipitation reaction: ${\text{Pb(NO}}_3{)}_2+2\text{KI}\to {\text{PbI}}_2+2{\text{KNO}}_3$, the yellow precipitate being lead iodide.

    Step-by-step solution →
18. Q238 CBSE 2023
    What ​is observed when ​aqueous solutions ​of ​potassium ​iodide ​and lead nitrate are mixed together ? ​Name the type of reaction and write the chemical equation for the reaction that occurs.
    Show answer

    A yellow precipitate of lead iodide forms in a double displacement (precipitation) reaction.

    A bright yellow precipitate of lead iodide is seen, which settles at the bottom. The reaction is a double displacement reaction (also called a precipitation reaction). $2\text{KI (aq)}+{\text{Pb(NO}}_3{)}_2\text{(aq)}\to {\text{PbI}}_2\text{(s, yellow)}+2{\text{KNO}}_3\text{(aq)}$

    Step-by-step solution →
19. Q239 CBSE 2023
    What ​is ​a balanced chemical ​equation? Why ​do ​we balance ​chemical equations?
    Show answer

    A balanced equation has equal atoms of each element on both sides; equations are balanced because mass is conserved.

    A balanced chemical equation is one in which the number of atoms of each element is equal on both sides of the equation, as in $3\text{Fe}+4{\text{H}}_2\text{O}\to {\text{Fe}}_3{\text{O}}_4+4{\text{H}}_2$. We balance chemical equations because of the law of conservation of mass: matter can neither be created nor destroyed in a chemical reaction, so the total mass, and hence the number of atoms of every element, must be the same before and after the reaction.

    Step-by-step solution →
20. Q240 CBSE 2023
    Give ​one example each of the ​reaction in which :

    1. (i)a more reactive metal displaces ​a ​less ​reactive metal from its ​aqueous salt solution and the colour of the solution changes.
    2. (ii)an insoluble ​precipitate is ​formed.
    Show answer

    Iron in copper sulphate solution turns it from blue to pale green; barium chloride with sodium sulphate gives a white precipitate.

    (i) Displacement with a colour change - an iron nail dipped in blue copper sulphate solution: $\text{Fe}(s)+{\text{CuSO}}_4(aq)⟶{\text{FeSO}}_4(aq)+\text{Cu}(s)$. The blue colour of the solution changes to pale green and reddish-brown copper is deposited on the nail. (ii) Formation of an insoluble precipitate - sodium sulphate solution added to barium chloride solution: ${\text{Na}}_2{\text{SO}}_4(aq)+{\text{BaCl}}_2(aq)⟶{\text{BaSO}}_4(s)\downarrow +2\text{NaCl}(aq)$. A white precipitate of barium sulphate is formed.

    Step-by-step solution →