Important Questions Class 12 Chemistry Chapter 4

Important Questions Class 12 Chemistry Chapter 4 focus on The d - and f - Block Elements, one of the most conceptual and scoring chapters in the Class 12 Chemistry syllabus. For the 12th Chemistry board exam (February 28, 2026), students must prioritise revision of high-weightage inorganic chemistry topics from this unit.

This chapter explains electronic configuration, general properties of transition elements, oxidation states, lanthanoids, actinoids, and their chemical behavior.

Questions are frequently asked in both short-answer and long-answer formats, along with conceptual MCQs. Practicing The d - and f - Block Elements Class 12 Important Questions ensures strong theoretical understanding and better retention before the final exam.

Important Questions Class 12 Chemistry Chapter 4 – The d - and f - Block Elements

The chapter The d - and f - Block Elements requires clear understanding of periodic trends and chemical properties. Students should thoroughly practice The d - and f - Block Elements Class 12 Important Questions, especially explanations related to variable oxidation states, formation of colored compounds, magnetic behavior, and lanthanoid contraction. Many board exam questions test conceptual reasoning, so writing precise and well-structured answers is important.

Below are exam-oriented Important Questions Class 12 Chemistry Chapter 4 covering short-answer, long-answer, and reasoning-based questions.

1. Which of the following oxidation state is common for lanthanides?

(1) +2
(2) +3
(3) +4
(4) +5

Sol. (3)

2. Account for the following trends in atomic and ionic radii of transition elements.

a) Ions of the same charge in a given series (3d, 4d or 5d) show progressive decrease in radii with increasing atomic number.

b) The atomic radii of elements in 4d series are more than that of corresponding elements in 3d series.

c) The atomic radii of the corresponding elements in 4d series and 5d series are virtually the same. [March 2013]

Sol. a) This is due to the poor shielding effect and increase in nuclear charge.

b) This is due to increase in no. of shells and greater shielding effect.

c) This is due to Lanthanoid contraction.

3.

Sol. Zero

4. What is the magnetic moment of an atom having d10 configuration?

Sol. 

5. Among the following transition elements which one has a completely filled d orbital?

(1) Ag
(2) Ti
(3) Mo
(4) Ni

Sol. (1)

6. Write the preparation of K2Cr2O7 from Chromite ore. [March 2023]

Sol. Potassium dichromate is generally prepared from chromite ore (FeCr2O4). The preparation involves three steps.

1. Conversion of chromite ore to sodium chromate. Chromite ore is first fused with sodium carbonate in presence of air to form sodium chromate.

2. Acidification of sodium chromate to sodium dichromate. The yellow solution of sodium chromate is filtered and acidified with sulphuric acid to orange sodium dichromate.

3. Conversion of sodium dichromate to potassium dichromate. The solution of sodium dichromate is treated with potassium chloride so that orange crystals of potassium dichromate crystallise out.

37. What is lanthanoid contraction? What are the consequences of lanthanoid contraction? [March 2024]

Sol. The regular decrease in the atomic and ionic radii along lanthanide series is known as lanthanide contraction. It is due to the poor shielding effect of f – electrons and increase in nuclear charge. Due to lanthanoid contraction, Zr and Hf have similar radii and hence similar physical properties. So their separation is difficult.

38.

Sol. i) Transition elements are all metals, they show variable oxidation states, they form coloured compounds and most of them are paramagnetic.

(ii) This is due to the extra stability of Cr3+ and Mn2+ ions

 39. Potassium dichromate is a very useful oxidizing agent.

(i) Name the ore of Potassium dichromate.
(ii) Explain the preparation of Potassium dichromate from Sodium chromate.

Sol.

(ii) First sodium chromate is acidified with sulphuric acid to produce sodium dichromate.

Then the solution of sodium dichromate is treated with potassium chloride so that orange crystals of potassium dichromate crystallise out.

40. The transition element present in ‘bronze’ is _____

Sol. Cu

Last-Minute Revision Tips for The d - and f - Block Elements

With limited time before the Chemistry board exam, follow these strategies:

1. Revise electronic configurations of transition elements daily.

2. Memorize important oxidation states and exceptions.

3. Focus on reasons for color and magnetic properties.

4. Revise lanthanoid contraction and its consequences carefully.

5. Practice previously solved The d - and f - Block Elements Class 12 Chemistry Important Question sets.

6. Avoid new material; concentrate only on revision of Important Questions Class 12 Chemistry Chapter 4.

5 Mistakes Students Make in The d- and f-Block Elements

1. Writing wrong electronic configurations.

2. Forgetting to mention unpaired electrons in magnetic property answers.

3. Not explaining why colour appears (d–d transitions).

4. Confusing lanthanoid contraction causes and consequences.

5. Missing units or incomplete reasoning in theory answers.