Chemistry · Electrochemistry · chapter 2 of 10

Class 12 Chemistry Chapter 2: Electrochemistry Assertion-reason questions with answers

2 assertion-reason questions on Electrochemistry, each with its answer and the reason, written from the NCERT chapter. For the CBSE board, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): Under standard conditions hydrogen ions can oxidise zinc but not copper. Reason (R): E°(Zn²⁺|Zn) is negative and E°(Cu²⁺|Cu) is positive with respect to the standard hydrogen electrode.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both are true. A metal with E° below zero reduces H⁺; one with E° above zero cannot. The signs of the two potentials are exactly why H⁺ oxidises Zn and not Cu.

Question 2
Assertion (A): A mercury cell gives a nearly constant voltage throughout its life. Reason (R): Mercury cells are used in hearing aids and watches.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Both are true, but the voltage is constant because no ion in solution changes concentration during the overall reaction, not because of where the cell is used.

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