ChemistryCBSE Class 12 · Sample paper, session 2026-27 · 2 marks · Very short answer

CBSE Class 12 Chemistry sample paper 2026-27: question 21

From the official CBSE sample question paper for 2026-27, section B, question 21, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q21 · 2 marks · Very short answerElectrochemistry

Account for the following:
(I) Underground iron pipelines are often protected by connecting them to a more reactive metal like magnesium. (1)
(II) Write the reactions occurring at cathode and anode during the electrolysis of molten magnesium chloride. (1)

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

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

Hint 1

Which metal is oxidised more easily, Mg or Fe?

Hint 2

In a melt, only $M g^{2 +}$ and $C l^{-}$ ions are present. Which is reduced and which is oxidised?

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.

(I) Mg is more reactive (more negative $E^{\circ}$ ) than Fe, so it acts as a sacrificial anode and is oxidised in place of iron: $M g \to M g^{2 +} + 2 e^{-}$ . The electrons flow to the iron pipe, which becomes the cathode and is not oxidised. This prevents corrosion. The Mg block is replaced from time to time.
1 mark
(II) Cathode: $M g^{2 +} + 2 e^{-} \to M g (l)$
½ mark
Anode: $2 C l^{-} \to C l_{2} (g) + 2 e^{-}$
½ mark

Answer: (I) Sacrificial protection: Mg oxidises instead of Fe; (II) Cathode: $M g^{2 +} + 2 e^{-} \to M g (l)$ ; Anode: $2 C l^{-} \to C l_{2} (g) + 2 e^{-}$

Where the marks are

Explains that Mg acts as a sacrificial anode and iron as the cathode (1 mark)
Cathode reaction (½ mark)
Anode reaction (½ 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 paperSample paper 2026-27: every question, by section.

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CBSE Class 12 Chemistry sample paper 2026-27: question 21

Hints

Step-by-step solution

Revise the chapter

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