ChemistryCBSE Class 12 · Sample paper, session 2026-27 · 3 marks · Short answer

CBSE Class 12 Chemistry sample paper 2026-27: question 22

From the official CBSE sample question paper for 2026-27, section C, question 22, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q22 · 3 marks · Short answerThe d- and f-Block Elements

(I) Which of the following has the highest magnetic moment? Justify your answer.
$T i^{2 +}, C o^{2 +}, F e^{2 +}$ .
[ Atomic No. Ti = 22, Co = 27, Fe = 26 ] (1)

(II) Which characteristic of iron make it suitable to:
a) act as catalyst in Haber’s process.
b) form interstitial compound with oxygen. (2)

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

Write the 3d configuration of each ion. Remember the 4s electrons are removed first.

Hint 2

Magnetic moment depends on the number of unpaired electrons.

Hint 3

For (II), think about the properties that make transition metals good catalysts and the spaces in their crystal lattices.

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) Configurations: $T i^{2 +}$ : $3 d^{2}$ (2 unpaired); $C o^{2 +}$ : $3 d^{7}$ (3 unpaired); $F e^{2 +}$ : $3 d^{6}$ (4 unpaired).
½ mark
$F e^{2 +}$ has the most unpaired electrons, so it has the highest magnetic moment: $μ = n (n + 2) = 24 = 4.90$ BM.
½ mark
(II)(a) Iron can show variable oxidation states and offers a large surface area for adsorption of $N_{2}$ and $H_{2}$ . These features help it catalyse ammonia formation in Haber's process.
1 mark
(II)(b) The iron crystal lattice has interstitial voids large enough to trap small non-metal atoms such as O, C or N. This gives interstitial compounds.
1 mark

Answer: (I) $F e^{2 +}$ (4 unpaired e⁻, μ ≈ 4.90 BM); (II)(a) variable oxidation states and large surface area; (b) interstitial voids in the lattice that fit small atoms.

Where the marks are

Correct configurations / unpaired electrons (½ mark)
Chooses $F e^{2 +}$ with justification (½ mark)
Variable oxidation states / large surface area for catalysis (1 mark)
Interstitial sites in the lattice accommodate small atoms (1 mark)

Revise the chapter

Chapter: The d- and f-Block Elements (notes, formulas, where marks are lost and every past question)

Practise this chapterBoard-style questions from The d- and f-Block Elements, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2026-27: 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.

CBSE Class 12 Chemistry sample paper 2026-27: question 22

Hints

Step-by-step solution

Revise the chapter

More questions from The d- and f-Block Elements