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Four half reactions I to IV… (Class 12 Chemistry 2023, Q4)

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ChemistryCBSE Class 12 · Board exam 2023, set 56/5/1 · 1 mark · MCQ

CBSE Class 12 Chemistry 2023: question 4

Set in the CBSE Class 12 board exam of 2023, paper 56/5/1, section A, question 4, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q4 · 1 mark · MCQElectrochemistry

Four half reactions I to IV are shown below :
I.
II.
III.
IV.
Which two of these reactions are most likely to occur when concentrated brine is electrolysed ?

  1. (A)I and III
  2. (B)I and IV
  3. (C)II and III
  4. (D)II and IV

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 56/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Electrolysis of brine gives chlorine gas at one electrode.

Hint 2

Water is reduced more easily than .

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. In concentrated brine, is oxidised at the anode in preference to (because of overpotential), giving .

  2. At the cathode, (from water) is reduced to rather than to Na. So reactions I and IV occur.

    1 mark

Answer: (B) I and IV

Where the marks are

  • Identifies reactions I and IV (1 mark)

Revise the chapter

  • Chapter: Electrochemistry (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Electrochemistry, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 56/5/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.