CBSE Class 12 Chemistry Exam 2025: Most Repeated Questions and Important Topics

Introduction

The CBSE Class 12 Chemistry exam is one of the most crucial subjects for science students, playing a significant role in their academic and competitive exam journey. Understanding the most frequently asked questions can help students prepare efficiently, revise important topics, and score high marks. Based on an analysis of previous years’ question papers, we have compiled a list of the most repeated questions from Chemistry for the CBSE Class 12 Chemistry Exam 2025, along with their answers. Reviewing these will help students grasp fundamental concepts, strengthen problem-solving skills, and enhance their overall performance.

Importance of Practicing Repeated Questions

Enhances Understanding: Repeated questions are often based on fundamental concepts that are essential for mastering Chemistry.
Improves Problem-Solving Skills: Practicing these questions allows students to apply theoretical knowledge in a structured manner.
Boosts Confidence: Familiarity with commonly asked questions reduces exam stress and builds confidence.
Optimizes Time Management: Knowing expected questions helps in planning time efficiently during the exam.

CBSE Class 12 Chemistry 2025 Most Repeated Questions and Answers

Physical and Chemical Changes

What is the difference between physical and chemical changes? Explain with examples.
Answer: A physical change alters only the appearance of a substance, without changing its composition, such as melting ice. A chemical change results in the formation of a new substance, such as rusting iron.

Equilibrium in Chemical Reactions

Explain the concept of equilibrium in chemical reactions. How does Le Chatelier’s Principle affect chemical equilibrium?
Answer: Chemical equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction. Le Chatelier’s Principle states that if an external change is applied to a system at equilibrium, the system adjusts to counteract the change, such as shifting equilibrium upon adding a reactant.

Periodic Table Trends

What happens to the size of atoms in p-block elements when moving from left to right in the same period?
Answer: (d) Size decreases due to increasing nuclear charge, pulling electrons closer to the nucleus.

Hybridization

Describe the concept of hybridization and its types. Give examples of sp, sp2, and sp3 hybridization.
Answer: Hybridization is the mixing of atomic orbitals to form new hybrid orbitals. Examples include:
- sp Hybridization: Linear molecules (e.g., BeCl2)
- sp2 Hybridization: Trigonal planar molecules (e.g., BF3)
- sp3 Hybridization: Tetrahedral molecules (e.g., CH4)

Chemical Bonding

What is the difference between ionic and covalent bonds? Provide examples.
Answer: Ionic bonds involve electron transfer (e.g., NaCl), while covalent bonds involve electron sharing (e.g., H2O).

Periodic Table Significance

Explain the significance of periodic table trends, such as atomic radius and electronegativity.
Answer: Atomic radius decreases across a period and increases down a group. Electronegativity follows the opposite trend, increasing across a period and decreasing down a group.

Isomerism in Organic Chemistry

What are isomers? Differentiate between structural and stereoisomers with examples.
Answer: Isomers are compounds with the same molecular formula but different structures. Structural isomers differ in connectivity (e.g., butane and isobutane), while stereoisomers have the same connectivity but different spatial arrangements (e.g., cis-trans isomers).

Acid-Base Chemistry

Define pH and explain its significance in chemistry. How does the pH scale work?
Answer: pH measures the hydrogen ion concentration in a solution. It ranges from 0-14, with acidic solutions having pH < 7, neutral solutions at pH 7, and basic solutions having pH > 7.

Types of Chemical Reactions

What are the different types of chemical reactions? Provide examples. What is the role of catalysts in chemical reactions?
Answer: Types of chemical reactions include:
- Combination Reactions: A + B → AB (e.g., 2H2 + O2 → 2H2O)
- Decomposition Reactions: AB → A + B (e.g., 2H2O2 → 2H2O + O2)
- Displacement Reactions: A + BC → AC + B (e.g., Zn + CuSO4 → ZnSO4 + Cu)
- Redox Reactions: Involves oxidation and reduction (e.g., Fe + O2 → Fe2O3) Catalysts speed up reactions without being consumed, such as enzymes in biological systems.

Coordination Chemistry

A Lewis acid is a species that has the ability to receive an electron pair. Lewis acids are all cations. It is a Lewis acid because the core atom of a coordination complex is a metal and always accepts electrons.Which of the following has a coordination number as a feature?
- a) Coordination entity
- b) Ligand
- c) Central atom
- d) Coordination compound

Answer: (d) Coordination compound, as the coordination number defines the number of ligand attachments to the central metal atom.

Preparation Tips for CBSE Class 12 Chemistry Exam 2025

Refer to NCERT Books: NCERT textbooks are the primary source for CBSE exams. Ensure thorough revision of all chapters.
Solve Previous Years’ Papers: Practicing past papers helps in understanding the exam pattern and important topics.
Take Mock Tests: Timed practice tests enhance speed and accuracy.
Make Short Notes: Jot down key formulas, definitions, and concepts for quick revision.
Understand Marking Scheme: Focus on high-weightage chapters and frequently asked topics.
Clarify Doubts: Seek help from teachers or online resources if any concept is unclear.

Conclusion

Studying the most repeated questions in Chemistry for CBSE Class 12 helps students focus on important concepts, improve their problem-solving ability, and manage time effectively during exams. Regular practice, conceptual clarity, and strategic preparation are key to scoring well in the 2025 Chemistry exam. Stay dedicated, revise consistently, and aim for excellence!

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