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GATE 2026 CY – Question 47

Physical Chemistry · Electrochemistry: Standard electrode potential and electrochemical cells. Nernst Equation and its application, relationship between electrode potential and thermodynamic quantities, Potentiometric and conductometric titrations. Ionic mobility and conductivity. Kohlrausch’s law, Debye-Hückel limiting law. Debye-Hückel- Onsager equation. · 2 marks · Multiple choice

For the following electrochemical cells, liquid junction potentials affect the cell potential (Ecell). The correct order of their Ecell at 25 °C is

Three electrochemical cells with KCl, NaCl and HCl liquid junctions.
  1. I > II > III
  2. II > I > III
  3. III = I > II
  4. II > I = III

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Correct answer: (B) II > I > III

Explanation

Fast H+ diffusion from concentrated to dilute HCl gives the largest positive right-side junction potential in II. In I, potassium moves right faster than sodium moves left, giving a smaller positive junction. In III fast H+ moves left and makes the right side negative.

Official GATE 2026 answer key: https://gate2026.iitg.ac.in/doc/download/2026/Keys/CY_Keys.pdf