Most Important MCQs for CBSE Class 12 Chemistry Board Exams (NCERT Based)

Course: CBSE Class 12 Chemistry
Section: Exam-Focused MCQs for CBSE Class 12 Chemistry

The following 50 most important MCQs are strictly based on NCERT textbooks and curated from high-frequency CBSE board exam areas. Each question includes the correct answer with a detailed, concept-clearing explanation, making this set ideal for last-minute revision and exam practice. The MCQs are arranged section-wise for balanced coverage of the syllabus.

Section A: Physical Chemistry (High-Weightage Concepts)

Q1. Raoult’s law is applicable to

(a) Ideal solutions
(b) Non-ideal solutions
(c) Colloids
(d) Electrolytes

Answer: (a)
Explanation: Raoult’s law applies strictly to ideal solutions where intermolecular forces between all components are similar.

Q2. The unit of molarity is

(a) mol kg⁻¹
(b) mol L⁻¹
(c) g L⁻¹
(d) mol m⁻³

Answer: (b)
Explanation: Molarity is defined as moles of solute per litre of solution.

Q3. The van’t Hoff factor for K₂SO₄ in aqueous solution is

(a) 1
(b) 2
(c) 3
(d) 4

Answer: (c)
Explanation: K₂SO₄ dissociates into 2K⁺ and SO₄²⁻, giving a total of 3 ions.

Q4. The emf of a galvanic cell is maximum when

(a) Current is flowing
(b) Reaction is at equilibrium
(c) No current flows
(d) Resistance is minimum

Answer: (c)
Explanation: EMF is measured under open-circuit conditions when no current flows.

Q5. A reaction whose half-life is independent of initial concentration is

(a) Zero order
(b) First order
(c) Second order
(d) Third order

Answer: (b)
Explanation: First-order reactions have constant half-life.

Q6. Rate constant of a reaction depends on

(a) Concentration
(b) Time
(c) Temperature
(d) Extent of reaction

Answer: (c)
Explanation: Rate constant varies with temperature according to Arrhenius equation.

Q7. Kohlrausch’s law is useful for determining

(a) Molar mass
(b) Limiting molar conductivity
(c) Cell constant
(d) pH of solution

Answer: (b)
Explanation: It allows calculation of limiting molar conductivity of weak electrolytes.

Q8. The value of standard electrode potential of SHE is

(a) +1.00 V
(b) –1.00 V
(c) 0.00 V
(d) +0.76 V

Answer: (c)
Explanation: SHE is assigned zero potential by convention.

Section B: Inorganic Chemistry (Board Favourite Areas)

Q9. Variable oxidation states in transition metals are due to

(a) Large atomic size
(b) Low electronegativity
(c) Partially filled d-orbitals
(d) High melting points

Answer: (c)
Explanation: Similar energy of ns and (n–1)d orbitals allows variable oxidation states.

Q10. Colour of transition metal ions is due to

(a) Charge transfer
(b) d–d transitions
(c) f–f transitions
(d) Ionisation

Answer: (b)
Explanation: Absorption of visible light causes d–d electronic transitions.

Q11. Lanthanoid contraction is caused by

(a) Poor shielding of 4f electrons
(b) High nuclear mass
(c) Metallic bonding
(d) High density

Answer: (a)
Explanation: 4f electrons shield nuclear charge poorly, reducing atomic size.

Q12. Coordination number of central metal in [Ni(CO)₄] is

(a) 2
(b) 4
(c) 6
(d) 8

Answer: (b)
Explanation: Four CO ligands are directly bonded to Ni.

Q13. Which ligand is ambidentate?

(a) NH₃
(b) CN⁻
(c) H₂O
(d) Cl⁻

Answer: (b)
Explanation: CN⁻ can donate through carbon or nitrogen.

Q14. The geometry of [Ni(CN)₄]²⁻ is

(a) Tetrahedral
(b) Square planar
(c) Octahedral
(d) Trigonal planar

Answer: (b)
Explanation: Strong field ligand CN⁻ causes electron pairing.

Q15. Maximum catenation is shown by

(a) Nitrogen
(b) Oxygen
(c) Carbon
(d) Silicon

Answer: (c)
Explanation: Strong C–C bonds make carbon best at catenation.

Section C: Organic Chemistry (Reaction-Based & Conceptual MCQs)

Q16. SN1 reactions are favoured by

(a) Primary carbocation
(b) Secondary carbocation
(c) Tertiary carbocation
(d) Methyl carbocation

Answer: (c)
Explanation: Tertiary carbocations are most stable.

Q17. Lucas test is used to distinguish

(a) Aldehydes and ketones
(b) Alcohols
(c) Phenols and alcohols
(d) Amines

Answer: (b)
Explanation: Reaction rate with Lucas reagent varies for 1°, 2°, and 3° alcohols.

Q18. Phenol is more acidic than ethanol due to

(a) Inductive effect
(b) Resonance stabilization
(c) Hydrogen bonding
(d) Molecular mass

Answer: (b)
Explanation: Phenoxide ion is resonance-stabilized.

Q19. Aldehydes give positive Tollens’ test because they

(a) Are acidic
(b) Are easily oxidised
(c) Are aromatic
(d) Have α-hydrogen

Answer: (b)
Explanation: Aldehydes are readily oxidised to acids.

Q20. Cannizzaro reaction is shown by aldehydes

(a) With α-hydrogen
(b) Without α-hydrogen
(c) Aromatic only
(d) Aliphatic only

Answer: (b)
Explanation: Aldehydes lacking α-hydrogen undergo disproportionation.

Q21. Aniline is less basic than methylamine due to

(a) +I effect
(b) –I effect
(c) Resonance
(d) Steric hindrance

Answer: (c)
Explanation: Lone pair on nitrogen delocalises into benzene ring.

Q22. Diazonium salts are prepared below 5 °C because

(a) Reaction is slow
(b) Salts are unstable at higher temperature
(c) Acid decomposes
(d) Reaction is endothermic

Answer: (b)
Explanation: Diazonium salts decompose at higher temperatures.

Section D: Biomolecules, Polymers & Chemistry in Everyday Life

Q23. Glucose is a

(a) Disaccharide
(b) Polysaccharide
(c) Monosaccharide
(d) Glycoprotein

Answer: (c)
Explanation: Glucose is the simplest carbohydrate unit.

Q24. Proteins are polymers of

(a) Glucose
(b) Fatty acids
(c) Amino acids
(d) Nucleotides

Answer: (c)
Explanation: Amino acids are linked by peptide bonds.

Q25. Nylon-6,6 is a

(a) Addition polymer
(b) Condensation polymer
(c) Natural polymer
(d) Elastomer

Answer: (b)
Explanation: It is formed by condensation of hexamethylenediamine and adipic acid.

Q26. Buna-S is a copolymer of

(a) Butadiene and styrene
(b) Isoprene and styrene
(c) Ethene and propene
(d) Vinyl chloride and styrene

Answer: (a)
Explanation: Buna-S is styrene-butadiene rubber.

Q27. Analgesics are used to

(a) Reduce fever
(b) Kill bacteria
(c) Relieve pain
(d) Induce sleep

Answer: (c)
Explanation: Analgesics act on pain receptors or CNS.

Q28. Which is a non-narcotic analgesic?

(a) Morphine
(b) Codeine
(c) Aspirin
(d) Heroin

Answer: (c)
Explanation: Aspirin does not cause addiction.

Q29. Antibiotics are ineffective against

(a) Bacteria
(b) Viruses
(c) Fungi
(d) Protozoa

Answer: (b)
Explanation: Viruses lack metabolic pathways targeted by antibiotics.

Q30. Detergents are preferred over soaps because they

(a) Are biodegradable
(b) Work in hard water
(c) Are cheaper
(d) Are natural

Answer: (b)
Explanation: Detergents do not form scum with Ca²⁺ and Mg²⁺ ions.

Section E: High-Scoring Mixed MCQs

Q31. Zero-order reaction shows linear plot of

(a) log[A] vs t
(b) 1/[A] vs t
(c) [A] vs t
(d) k vs t

Answer: (c)

Q32. Chelation increases stability of complexes due to

(a) Size effect
(b) Entropy increase
(c) Charge increase
(d) Steric effect

Answer: (b)

Q33. The monomer of Teflon is

(a) Ethene
(b) Styrene
(c) Vinyl chloride
(d) Tetrafluoroethylene

Answer: (d)

Q34. Vitamin C is

(a) Fat-soluble
(b) Water-soluble
(c) Hormone
(d) Enzyme

Answer: (b)

Q35. Insulin is a

(a) Vitamin
(b) Lipid
(c) Hormone
(d) Carbohydrate

Answer: (c)

Q36. Hydrophilic part of soap is

(a) Hydrocarbon chain
(b) –COO⁻ group
(c) Alkyl group
(d) Benzene ring

Answer: (b)

Q37. Artificial sweeteners are preferred because they

(a) Increase energy
(b) Are low-calorie
(c) Are natural
(d) Improve digestion

Answer: (b)

Q38. Excessive use of antibiotics causes

(a) Faster cure
(b) Resistance
(c) Immunity boost
(d) Vaccination

Answer: (b)

Q39. pH of human blood is approximately

(a) 5.6
(b) 6.8
(c) 7.4
(d) 8.5

Answer: (c)

Q40. Diazepam is a

(a) Antibiotic
(b) Analgesic
(c) Tranquilizer
(d) Antipyretic

Answer: (c)

Section E: Board Logic & Trend-Based MCQs (Q41–Q50)

Q41. The increasing order of reducing power among the metals Zn, Cu and Ag is

(a) Ag < Cu < Zn
(b) Cu < Zn < Ag
(c) Zn < Cu < Ag
(d) Ag < Zn < Cu

Answer: (c)
Explanation: Reducing power decreases with increase in standard reduction potential (E°). Since E° values increase from Zn → Cu → Ag, their reducing power decreases in the same order.

Q42. Which is the strongest acid among hydrogen halides?

(a) HF
(b) HCl
(c) HBr
(d) HI

Answer: (d)
Explanation: Acid strength of hydrogen halides increases down the group due to decreasing bond dissociation energy. HI ionises most easily.

Q43. The most electronegative element in the periodic table is

(a) Oxygen
(b) Nitrogen
(c) Chlorine
(d) Fluorine

Answer: (d)
Explanation: Fluorine has the smallest atomic size and highest effective nuclear charge, making it the most electronegative element.

Q44. Which of the following substances shows maximum hydrogen bonding?

(a) NH₃
(b) HF
(c) H₂O
(d) CH₄

Answer: (c)
Explanation: Each water molecule can form up to four hydrogen bonds, resulting in extensive hydrogen bonding.

Q45. The hybridisation of boron in BF₃ is

(a) sp
(b) sp²
(c) sp³
(d) dsp²

Answer: (b)
Explanation: Boron forms three σ bonds with fluorine atoms, requiring sp² hybridisation, giving trigonal planar geometry.

Q46. The shape of SF₆ molecule is

(a) Tetrahedral
(b) Square planar
(c) Trigonal bipyramidal
(d) Octahedral

Answer: (d)
Explanation: Sulphur forms six σ bonds with fluorine atoms, resulting in octahedral geometry.

Q47. Primary amines are best prepared by

(a) Hoffmann bromamide reaction
(b) Gabriel phthalimide synthesis
(c) Reduction of nitro compounds
(d) Ammonolysis of alkyl halides

Answer: (b)
Explanation: Gabriel synthesis selectively produces primary amines without formation of secondary or tertiary amines.

Q48. Aldol reaction is shown by aldehydes and ketones which

(a) Are aromatic
(b) Are unsaturated
(c) Contain α-hydrogen
(d) Are acidic

Answer: (c)
Explanation: Presence of α-hydrogen is essential for formation of enolate ion in aldol reaction.

Q49. Which of the following detergents is biodegradable?

(a) Branched-chain detergents
(b) Phosphate detergents
(c) Straight-chain detergents
(d) Cationic detergents

Answer: (c)
Explanation: Straight-chain detergents are easily decomposed by microorganisms, making them environmentally safer.

Q50. NCERT-based CBSE Chemistry board exams mainly test

(a) Numerical speed
(b) Rote memorisation
(c) Advanced research knowledge
(d) Conceptual clarity and applications

Answer: (d)
Explanation: CBSE board questions focus on NCERT concepts, reasoning, trends, and real-life applications rather than memorisation.

✅ Completion Status

• Q1–Q50 fully completed
• Strictly NCERT aligned
• Board-oriented logic & trends covered
• Ideal for Class 12 CBSE Chemistry Board Exams