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NCERT Exemplar · Class 11 · Chemistry

Chapter 8: Redox Reactions

Practice each question, then open the answer or worked solution.

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Short Answer Questions

16 questions
Q27Written answer

Match Column I with Column II for the oxidation states of the central atoms. 


Column I

Column II

\[\left( \mathbf{i} \right)\text{ }\mathbf{C}{{\mathbf{r}}_{\mathbf{2}}}{{\mathbf{O}}_{\mathbf{7}\text{ }}}^{\mathbf{2}}\]

(a) + 3

\[\left( \mathbf{ii} \right)\text{ }\mathbf{Mn}{{\mathbf{O}}_{\mathbf{4}}}^{}\]

(b) + 4

\[\left( \mathbf{iii} \right)\text{ }\mathbf{V}{{\mathbf{O}}_{\mathbf{3}}}^{}\]

(c) + 5

\[\left( \mathbf{iv} \right)\text{ }\mathbf{Fe}{{\mathbf{F}}_{\mathbf{6}}}^{\mathbf{3}}\]

(d) + 6


(e) + 7 


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Worked solution

Ans: (i) \[\to \] (d); (ii) \[\to \] (e); (iii) \[\to \] (c); (iv) \[\to \] (a)


Q28Written answer

Match the items in Column I with relevant items in Column II. 

Column I

Column II

(i) Ions having positive charge

(a) +7

(ii) The sum of oxidation number of all atoms in a neutral molecule.

(b) –1 

(iii) Oxidation number of hydrogen ion (H+).

(c) +1

(iv) Oxidation number of fluorine in NaF.

(d) 0

(v) Oxidation number of fluorine in NaF.

(e) Cation


(f) Anion


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Worked solution

Ans:  (i) \[\to \] (e); (ii) \[\to \] (d); (iii) \[\to \] (c); (iv) \[\to \] (b); (v) \[\to \] (f).


Assertion and Reason Type

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.


Q29Written answer

Assertion (A): Among halogens fluorine is the best oxidant. 

Reason (R): Fluorine is the most electronegative atom. 

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

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false. 

(iv) Both A and R are false. 

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Worked solution

Ans: Fluorine is most electronegative element that is why it is best oxidant among halogens. Option (i) is the correct answer.


Q30Written answer

Assertion (A): In the reaction between potassium permanganate and potassium iodide, permanganate ions act as oxidising agent. 

Reason (R): Oxidation state of manganese changes from +2 to +7 during the reaction. 

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

(ii) Both A and R are true but R is not the correct explanation of A. 

(iii)A is true but R is false. 

(iv) Both A and R are false.

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Worked solution

Ans: As permanganate ion changes to \[\text{Mn}{{\text{O}}_{\text{2}}}\]. Option(iii) is the correct answer.


Q31Written answer

Assertion(A): The decomposition of hydrogen peroxide to form water and oxygen is an example of disproportionate reaction. 

Reason (R): The oxygen of peroxide is in -1 oxidation state and it is converted to zero oxidation state in O2 and -2 oxidation state in H2O.

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

(ii) Both A and R are true but R is not the correct explanation of A. 

(iii) A is true but R is false. 

(iv) Both A and R are false. 

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Worked solution

Ans: Here the oxygen of peroxide, which is present in -1 state, is converted to zero oxidation state in O2 undergoing oxidation and decreases to -2 oxidation state in H2O undergoing reduction. Option (i) is the correct answer.


Q32Written answer

Assertion (A): Redox couple is the combination of oxidised and reduced form of a substance involved in an oxidation or reduction half-cell. 

Reason (R): In the representation, \[{{\mathbf{E}}^{\odot }}_{\mathbf{F}{{\mathbf{e}}^{\mathbf{3+}}}\mathbf{/ F}{{\mathbf{e}}^{\mathbf{2+}}}}\] and \[{{\mathbf{E}}^{\odot }}{{\mathbf{ }}_{\mathbf{C}{{\mathbf{u}}^{\mathbf{+2}}}\mathbf{/Cu}}},\,{{\mathbf{E}}^{\odot }}_{\mathbf{F}{{\mathbf{e}}^{\mathbf{3+}}}\mathbf{/ F}{{\mathbf{e}}^{\mathbf{2+}}}}\], Cu2+/Cu  are redox couples. 

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

(ii) Both A and R are true but R is not the correct explanation of A. 

(iii) A is true but R is false.

(iv) Both A and R are false. 

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Worked solution

Ans: A redox couple is defined as pair of compounds or elements having together the oxidised and reduced forms of it and taking part in an oxidation or reduction half reaction. Option(ii) is the correct answer.