CBSE Class 12 Chemistry Question Bank with Important Questions – d and f Block Elements Properties 2026
- Feb 13
- 4 min read
The CBSE Class 12 Chemistry Question Bank for the 2026 academic year is an essential resource for students aiming to decode the complexities of transition and inner-transition elements. The d and f block elements (Chapter 4) often carry a significant weightage of approximately 7 marks in the board examination. Understanding the unique properties of these elements—such as variable oxidation states, catalytic behavior, and the famous lanthanoid contraction—is not just vital for boards but also forms the backbone of medical entrance exams like NEET.
In this comprehensive guide, we analyze the most frequent question patterns, provide official resources for the 2026 session, and breakdown the core properties of these elements in a student-friendly format.
Why d and f Block Elements are Crucial for 2026 Boards
The study of d-block (Groups 3–12) and f-block (Lanthanoids and Actinoids) elements is unique because it transitions from general periodic trends to specific chemical behaviors. For the 2026 curriculum, the CBSE has emphasized competency-based questions that require students to apply concepts rather than just memorizing facts.
Key Highlights of the 2026 Syllabus:
Medical Relevance: Heavy focus on transition metals like Iron (Fe) in hemoglobin and Platinum (Pt) in anti-cancer drugs (Cisplatin).
Industrial Applications: Understanding the Contact process (V2O5) and Haber’s process (Fe).
Analytical Chemistry: Preparation and properties of K2Cr2O7 and KMnO4.
CBSE Class 12 Chemistry Question Bank: Core Properties & Trends
To excel in the CBSE Class 12 Chemistry Question Bank, you must master the horizontal and group trends of the 3d transition series. Here are the most high-yielding properties:
1. Electronic Configuration and Exceptions
Most transition elements follow the (n-1)d^{1-10} ns^{1-2} configuration. However, exceptions like Chromium (Cr) and Copper (Cu) are board favorites.
Cr (Z=24): [Ar] 3d^5 4s^1 (Half-filled stability)
Cu (Z=29): [Ar] 3d^{10} 4s^1 (Fully-filled stability)
2. Variable Oxidation States
Transition metals show a wide range of oxidation states because the energy difference between (n-1)d and ns orbitals is very small. Manganese (Mn) exhibits the maximum number of oxidation states in the 3d series, ranging from +2 to +7.
3. Formation of Coloured Ions
Color in transition metal ions arises due to d-d transitions. When ligands approach a metal ion, the d-orbitals split. Electrons absorbing light energy jump to higher energy levels, and the transmitted light gives the ion its characteristic color.
Note: Sc^3+ and Zn^2+ are colorless because they have d^0 and d^10 configurations, respectively (no unpaired electrons for transition).
4. Lanthanoid Contraction
This is the most repeated topic in the CBSE Class 12 Chemistry Question Bank. It refers to the steady decrease in atomic and ionic radii from Lanthanum to Lutetium.
Cause: Poor shielding effect of 4f electrons.
Consequence: Similar chemical properties of 4d and 5d series (e.g., Zr and Hf have almost identical sizes).
Important Questions for 2026 Board Exams
Based on the analysis of the last 10 years of CBSE papers and the latest 2026 sample trends, here are the "Must-Solve" questions.
Very Short Answer Type (1 Mark)
Why is the third ionization enthalpy of Manganese (Z=25) exceptionally high?
Which element of the 3d series has the lowest enthalpy of atomization and why? (Ans: Zinc, due to absence of unpaired electrons).
Define Interstitial Compounds.
Short Answer Type (2-3 Marks)
Explain the catalytic property of transition metals. Mention their role in the medical field (e.g., enzymes containing metal ions).
Compare Lanthanoids and Actinoids based on their oxidation states and radioactivity.
Why is Cu+ unstable in aqueous solution? (Ans: It undergoes disproportionation).
Case Study / Long Answer (5 Marks)
Describe the preparation of KMnO4 from pyrolusite ore (MnO2).
How does the pH of the solution affect the transition between chromate and dichromate ions? Write the chemical equations.
Official Links for CBSE Question Banks
CBSE Official Academic Portal: cbseacademic.nic.in
Official Link : https://www.cbse.gov.in/cbsenew/question_bank.html
Conclusion
Mastering the d and f block elements requires a balance between understanding the periodic trends and memorizing key reactions like those of K2Cr2O7. By utilizing a well-structured CBSE Class 12 Chemistry Question Bank, students can focus their energy on high-probability topics and ensure they are ready for both the 2026 Board exams and upcoming medical entrances. Start your revision by practicing the electronic configurations and the specific reasons behind the "anomalous" behaviors of these fascinating metals.
FAQ Section: CBSE Class 12 Chemistry Question Bank
Q1: What are the most important topics in the CBSE Class 12 Chemistry Question Bank for d and f block?
Answer: The most critical topics include Lanthanoid contraction and its consequences, variable oxidation states of Mn, the magnetic moment formula (Spin-only formula), and the preparation/oxidizing properties of KMnO4.
Q2: Why are Zn, Cd, and Hg not considered transition elements?
Answer: According to IUPAC, transition metals must have an incomplete d-subshell in their ground state or common oxidation states. Zinc, Cadmium, and Mercury have completely filled d^10 configurations, hence they are d-block elements but not transition metals.
Q3: Is the 2026 Question Bank different from previous years?
Answer: Yes, the CBSE Class 12 Chemistry Question Bank 2026 includes more competency-focused questions and case studies related to the application of elements in green chemistry and medicine.
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