Q30 of 37 Page 109

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.

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


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


The decomposition of hydrogen peroxide gives water and oxygen molecule as a product. The oxidation number of oxygen in peroxide is -1 and that of hydrogen is +1. Thus oxygen under consideration is reduced from -1 to -2 in H2O molecule whereas it is oxidized to zero in oxygen molecule.


Thus both statements are true, but the main driving force is reason that peroxide undergoes disproportionation reaction is due to the availability of more stable oxygen molecule and water form for the peroxide. Thus the statement two is not the correct explanation for the (A).


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28

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.

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.


 29

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.

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.


 31

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.

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 E° Fe3+/fe2+and E°cu2+/cu , Fe3+ / Fe2+ and Cu2+ 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


 32

Explain redox reactions on the basis of electron transfer. Give suitable examples.