CBSE Class 12 Chemistry Exam 2025-26: Most Important Questions with Answers for Last Minute Revision

The CBSE Class 12 Chemistry Board Exam is scheduled for tomorrow, February 28, 2026. Time is running out, and this last-minute revision should focus on practicing only those questions that are most likely to appear in the Board Exam.

We have prepared the most important CBSE questions with detailed answers. These questions cover all high-weight chapters. MCQs, Case Study-Based Questions, Short Answers, and Long Answers—important questions from every section are covered.

These questions have been selected based on previous year papers, CBSE sample papers, and expert opinions. This content will be very useful for last-minute revision. Check it now and strengthen your preparation.

CBSE Class 12 Chemistry Most Important Questions and Answers PDF

Important MCQs with Answers

Q1. When MnO₂ is fused with KOH in presence of air, it forms:

(A) KMnO₄

(B) K₂MnO₄

(C) Mn₂O₇

(D) Mn₂O₃

Q2. EDTA⁴⁻ acts as a:

(A) Monodentate ligand

(B) Bidentate ligand

(C) Tridentate ligand

(D) Polydentate ligand

Q3. The value of Henry's constant KH is: 

(A) Greater for gases with higher solubility 

(B) Greater for gases with lower solubility 

(C) Constant for all gases 

(D) Not related to the nature of the gas

Q4. Which compound contains sp² hybridised carbon bonded to X?

(A) CH₃–CH₂–X

(B) CH₂=CH–X

(C) CH₃–CH₂–CH₂–X

(D) CH₃–X

Q5. The most acidic compound among the following is:

(A) Phenol

(B) Ethanol

(C) Methanol

(D) Water

Q6. Anisole reacts with HI to give:

(A) Phenol + CH₃I

(B) Phenol + CH₃OH

(C) Iodobenzene

(D) Benzyl iodide

Q7. Ethanol heated with conc. H₂SO₄ at 413 K forms:

(A) Ethene

(B) Diethyl ether

(C) Ethyl hydrogen sulphate

(D) Acetaldehyde

Q8. An azeotropic mixture shows:

(A) No deviation from Raoult’s law

(B) Positive deviation

(C) Negative deviation

(D) Complete dissociation

Q9. If relative lowering of vapour pressure is 0.0225, mole fraction of solute is:

(A) 0.80

(B) 0.725

(C) 0.15

(D) 0.0225

Q10. During electrolysis of aqueous NaCl:

(A) H₂ is liberated at anode

(B) Na metal is formed at cathode

(C) Cl₂ gas is liberated at anode

(D) O₂ gas is liberated at cathode

Important Questions Case Study Questions

Case No.1: In general, there are two types of protein molecules: fibrous proteins and globular proteins. Fibrous proteins are insoluble and elongated. Globular proteins are soluble and compact. Fibrous and Globular proteins may comprise one or more types of protein structures, and they include primary, secondary, tertiary and quaternary structures. These structures are based on the level of complexity of the folding of a polypeptide chain.

Primary Structure: It is a specific sequence of amino acids. The order of amino acids bonded together is detected by information stored in genes.

Secondary Structure: It is the shape in which a long polypeptide chain can exist. It is formed by hydrogen bonds between the atoms along the backbone of the polypeptide chain.

Tertiary Structure: It is determined by R-groups. It is a three-dimensional shape of a protein. Many numbers of tertiary structure fold to form quaternary Structure.

Quaternary Structure: It is the arrangement of multiple folded protein subunits in a multi-subunit complex.

The following questions are multiple-choice questions. Choose the most appropriate answer:

(i) Beta-pleated sheets are an example of:

a) Primary Structure

b) Secondary Structure

c) Tertiary Structure

d) Quaternary Structure

Answer: b) Secondary Structure

(ii) Which of the following structures have hydrogen bonds between polypeptide chains arranged in parallel?

a) Primary structure

b) Alpha-helix structure

c) Beta-Pleated sheets

d) Tertiary structure

Answer: c) Beta-Pleated sheets

(iii) Which of the following statements are true about proteins?

a) Proteins are made up of amino acids.

b) Proteins are essential for the development of skin, teeth and bones.

c) Protein is the only nutrient that can build, repair and maintain body tissues.

d) All of the above

Answer: d) All of the above

(iv) What is a bond between amino acids called?

a) Ionic Bond

b) Peptide Bond

c) Hydrogen bond

d) Acidic bond

Answer: b) Peptide Bond

(v) A tripeptide has :

a) 3 amino acids and 1 peptide bond

b) 3 amino acids and 2 peptide bonds

c) 3 amino acids and 3 peptide bonds

d) 3 amino acids and 4 peptide bonds

Answer: b) 3 amino acids and 2 peptide bonds

Case No.2: In the hexagonal system of crystals, the arrangement of atoms is described as a hexagonal prism. In this, the top and bottom of the cell are arranged in regular hexagons along with the three atoms that are sandwiched in between them. The total number of atoms per unit cell in hcp is six. So, hexagonal close packing (hcp), is constituted of a sphere on a flat surface, which is hence surrounded in the same plane by the six identical spheres which are very close to each other. Three spheres are then placed over the first layer so that they touch each other which eventually represents the second layer. Each one of these three spheres touches three spheres of the bottom layer. Finally, the second layer is covered with a third layer that is identical to the bottom layer in relative position. Since the structure repeats itself after every two

layers, the stacking for hcp may be described as "ABAB.." The atoms in a hexagonal closest-packed structure efficiently occupy 74% of space.

Based on the above information, answer the following questions:

(i) Which of the following types of arrangement is present in hcp crystal structure?

(a) AAAA....

(b) ABAB...

(c) ABCABC....

(d) None of the above

Answer: (b) ABAB...

(ii) How much empty space is present in the hcp unit cell?

(a) 74%

(b) 47.6%

(c) 32%

(d) 26%

Answer: (d) 26%

(iii) Which of the following statements is correct about hexagonal close packing?

(a) In this arrangement, the second layer is identical to the first layer.

(b) The total number of atoms per unit cell is 6.

(c) It is as closely packed as body-centred cubic packing.

(d) Its packing efficiency is 68%.

Answer: (b) The total number of atoms per unit cell is 6.

Q.No.3: Read the passage given below and answer the following questions:

Aliphatic amines with low molecular masses are gases and have a fishy smell. Primary amines consisting of at least three carbon atoms exist in a liquid state whereas the higher ones are solid. Many aryl amines, including aniline, are colourless, but they show colour on atmospheric oxidation. Lower aliphatic amines form hydrogen bonds with water due to which they are soluble in water. Whereas the higher amines are insoluble in water due to the large size of the hydrophobic alkyl part. Considering the electronegativity of nitrogen of amine and oxygen of alcohol as 3.0 and 3.5, respectively, it can be anticipated that amines show lower solubility in water as compared to alcohols. The decreasing order of hydrogen bonding in amines is as follows:

Primary > Secondary > Tertiary

(i) What is the order of boiling points of isomeric amines?

(ii) Which class of amines have a fishy odour?

(iii) Why are higher amines insoluble in water?

(iv) Why is the intermolecular association more in primary amines than in secondary amines?

(v) Alcohols of comparable molecular masses have a higher boiling point than amines. Explain

Answer: 

(i) The order of boiling points of isomeric amines is as follows:

Primary > Secondary > Tertiary

(ii) The lower aliphatic amines are gases with a fishy odour.

(iii) Solubility decreases with an increase in the molar mass of amines due to an increase in the size of the hydrophobic alkyl part. Therefore, higher amines are essentially insoluble in water.

(iv) The intermolecular association is more in primary amines than in secondary amines because there are two hydrogen atoms available for hydrogen bond formation in it.

(v) The electronegativity of oxygen in alcohol is more than that of nitrogen amine. Thus, alcohols are more polar than amines and form stronger intermolecular hydrogen bonds than amines. Hence, the boiling points of alcohols of comparable molecular masses are higher than amines.

Important Questions Assertion and Reason Questions

Q. No.1: Assertion (A): Halogens are o, p-directing in electrophilic aromatic substitution reactions.

Reason (R): Usually, para product predominates in an electrophilic substitution reaction.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (b) Both A and R are true, and R is not the correct explanation of the assertion.

Q. No.2: Assertion (A): In Haber's process for the manufacture of ammonia, molybdenum acts as a promoter for iron.

Reason (R): Promoters are substances that enhance the activity of a catalyst.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (a) Both A and R are true, and R is the correct explanation of the assertion.

Q. No.3: Assertion (A): F— F bond in F2 molecule is weak.

Reason (R): The F atom is small in size, which leads to large electron-electron repulsions.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (a) Both A and R are true, and R is the correct explanation of the assertion.

Q. No. 4: Assertion (A): Molarity of a solution in the liquid state changes with temperature.

Reason (R): The volume of a solution changes with a change in temperature.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (a) Both A and R are true, and R is the correct explanation of the assertion.

Q. No. 5: Assertion (A): Alcohol and phenol can be distinguished by sodium hydroxide.

Reason (R): Phenol is acidic, while alcohol is neutral.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (a) Both A and R are true, and R is the correct explanation of the assertion.

Q. No. 6: Assertion (A): All amino acids exist as zwitter ions in aqueous solutions.

Reason (R): Amino acids have both -NH2(basic) and -COOH(acidic) groups.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (a) Both A and R are true, and R is the correct explanation of the assertion.

Q .No. 7: Assertion: Benzyl bromide, when kept in acetone and water, produces benzyl alcohol.

Reason: The reaction follows SN2 mechanism.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (c) A is true, but R is false.

Q. No. 8: Assertion (A): The boiling points of alkyl halides decrease in the order: RI> RBr> RCl > RF.

Reason (R): Fluorine is the most electronegative atom.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (b) Both A and R are true, and R is not the correct explanation of the assertion.

Q. No. 9: Assertion (A): Molality is regarded as a better criterion for measurement of concentration.

Reason (B): Molality is independent of temperature.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (a) Both A and R are true, and R is the correct explanation of the assertion.

Q. No. 10: Assertion (A): Glycine should be taken through diet.

Reason (R): Glycine is a non-essential amino acid.

(a) Both A and R are true, and R is the correct explanation of the assertion.

(b) Both A and R are true, and R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

Answer: (d) A is false, but R is true.

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👉 CBSE Class 12 Study Materials

CBSE Class 12 study material includes latest syllabus, sample papers, NCERT books and solutions, previous year question papers, chapter-wise important questions, case study questions, assertion-reason questions, and competency-based questions — all updated as per the latest CBSE board exam pattern.