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JEE Main 202623 JanuaryEvening Shift
Exam
JEE Main
Year
2026
Date
23 January
Shift
Evening Shift
Subject
Chemistry
Chapter
Electrochemistry

JEE Main 2026 · 23 January · Evening Shift · Chemistry · Electrochemistry

Consider the above electrochemical cell where a metal electrode (M)...

Consider the above electrochemical cell where a metal electrode (M) is undergoing redox reaction by forming M^ + (M
Consider the above electrochemical cell where a metal electrode (M) is undergoing redox reaction by forming M+(M→M++e−)\mathrm{M}^{+}\left(\mathrm{M} \rightarrow \mathrm{M}^{+}+\mathrm{e}^{-}\right). The cation M+\mathrm{M}^{+}is present in two different concentrations c1c_{1} and c2c_{2} as shown above. Which of the following statement is correct for generating a positive cell potential?

Options

  1. AIf c1\mathrm{c}_{1} is present at cathode, then c1<c2\mathrm{c}_{1}<\mathrm{c}_{2}.
  2. BIf c1\mathrm{c}_{1} is present at anode, then c1>c2\mathrm{c}_{1}>\mathrm{c}_{2}.
  3. CIf c1c_{1} is present at cathode, then c1>c2c_{1}>c_{2}.
  4. DIf c1\mathrm{c}_{1} is present at anode, then c1=c2\mathrm{c}_{1}=\mathrm{c}_{2}.

Correct answer

C. If c1c_{1} is present at cathode, then c1>c2c_{1}>c_{2}.

Step-by-step solution

The given setup is a concentration cell with identical electrodes (M) and different electrolyte concentrations (c1c_1 and c2c_2).
For a concentration cell, the standard cell potential Ecell0=0E^0_{cell} = 0.
The cell reactions are:
Anode: M(s)→M+(canode)+e−M(s) \rightarrow M^+(c_{anode}) + e^-
Cathode: M+(ccathode)+e−→M(s)M^+(c_{cathode}) + e^- \rightarrow M(s)
Net reaction: M+(ccathode)→M+(canode)M^+(c_{cathode}) \rightarrow M^+(c_{anode})
Using the Nernst equation at 298 K298\text{ K}:
Ecell=Ecell0−0.0591nlog⁡canodeccathodeE_{cell} = E^0_{cell} - \frac{0.0591}{n} \log \frac{c_{anode}}{c_{cathode}}
Ecell=0−0.0591log⁡canodeccathodeE_{cell} = 0 - 0.0591 \log \frac{c_{anode}}{c_{cathode}}
For a positive cell potential (Ecell>0E_{cell} > 0), the term log⁡canodeccathode\log \frac{c_{anode}}{c_{cathode}} must be negative.
This requires canodeccathode<1\frac{c_{anode}}{c_{cathode}} < 1, which means ccathode>canodec_{cathode} > c_{anode}.
If c1c_1 is present at the cathode and c2c_2 is at the anode, then for Ecell>0E_{cell} > 0, we must have c1>c2c_1 > c_2.
Checking the options:
(1)Ifc1If c_1 is at cathode, c1<c2c_1 < c_2 (Incorrect)
(2)Ifc1If c_1 is at anode, c1>c2c_1 > c_2 (Incorrect, would require c2>c1c_2 > c_1)
(3)Ifc1If c_1 is at cathode, c1>c2c_1 > c_2 (Correct)
(4)Ifc1If c_1 is at anode, c1=c2c_1 = c_2 (Incorrect, EcellE_{cell} would be zero)
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