CBSE Class 12 Chemistry Most Expected Questions 2025

Chemistry is one of the most crucial components of the CBSE Class 12 syllabus, often considered a subject that requires conceptual understanding and memorisation. While students prepare for their board exams, they often ask about which topics to focus on and how to optimise their preparation. This article contains an exhaustive list of important questions in Class 12 Chemistry along with practical tips on how to master the subject. Whether your objective is to achieve good grades or deepen your understanding, this study aid will serve as your roadmap.

Importance of Emphasis on Key Questions

Class 12 Chemistry covers vast material such as Physical Chemistry Organic Chemistry Inorganic Chemistry If you narrow your focus to important questions, which would seem a mountainside of toil, it will be interesting and make preparation a lot easier for you. Important questions will help you face frequently asked problems and prepare you for different formats of questioning, short answers, long answers, and application-based higher-order thinking skills (HOTS) questions.

Also Read: Avoid These Exam Day Blenders For CBSE 2025

Most Expected Questions

1.  Despite the long-range order in the arrangement of particles, why are the crystals usually not perfect?

2. Why does table salt, NaCl, sometimes appear yellow in colour?

3. Why does the electrical conductivity of semiconductors increase with a temperature rise?

4. A sample of ferrous oxide has the actual formula Fe0.93O1.00. In this sample what fractions of metal ions are Fe2+ ions? What type of non-stoichiometric defect is present in this sample?

5.  In a compound, nitrogen atoms (N) make cubic close-packed lattices and metal atoms (M) occupy one-third of the tetrahedral voids present. Determine the formula of the compound formed by M and N.

6.  Concentration terms such as mass percentage, ppm, mole fraction and molality are independent of temperature, however molarity is a function of temperature. Explain.

7.  Why is the vapour pressure of an aqueous solution of glucose lower than that of water?

8. Components of a binary mixture of two liquids A and B were separated by distillation. After some time separation of components stopped and the composition of the vapour phase became the same as that of the liquid phase. Both the components started coming in the distillate. Explain why this happened.

9. What is the significance of Henry’s Law constant KH?

10. How does sprinkling of salt help in clearing snow-covered roads in hilly areas? Explain the phenomenon involved in the process.

11. Aqueous copper sulphate solution and aqueous silver nitrate solution are electrolysed by 1-ampere current for 10 minutes in separate electrolytic cells. Will the mass of copper and silver deposited on the cathode be the same or different? Explain your answer.

12. The value of standard electrode potential for the oxidation of Cl– ions is more positive than that of water, even then in the electrolysis of aqueous sodium chloride, why are Cl– ions oxidised at anode instead of water?

13. Define the terms specific conductance, molar conductance and equivalent conductance. Derive the relationship between molar conductance and equivalent conductance.

14. State Kohlrausch’s law. How does the law help in calculating Λ0∞ CH3COOH?

15. State Faraday’s first law of electrolysis. How much charge in terms of Faraday is required for the reduction of 1 mole of Cu2+ ions to Cu?

16. State a condition under which a bimolecular reaction is kinetically a first-order reaction.

17.  For a reaction A + B → Products, the rate law is – Rate = k [A][B]3/2. Can the reaction be an elementary reaction? Explain.

18. Why is molecularity applicable only for elementary reactions and order is applicable for elementary as well as complex reactions?

19. All energetically effective collisions do not result in a chemical change. Explain with the help of an example.

20. With the help of an example explain what is meant by pseudo-first-order reaction.

21. Why is it important to have a clean surface in surface studies?

22. What causes Brownian motion in colloidal solution?

23. What is the role of adsorption in heterogeneous catalysis?

24. What do you understand by shape-selective catalysis? Why are zeolites good shape-selective catalysts?

25. What are the applications of adsorption in chemical analysis?

26. Why is an external emf of more than 2.2V required for the extraction of Cl₂ from brine?

27. Write two basic requirements for refining metal by the Mond process and by Van Arkel Method.

28. Write down the reactions taking place in Blast furnaces related to the metallurgy of iron in the temperature range of 500-800 K.

29. What is the role of flux in metallurgical processes?

30. Explain the following: (a) CO₂ is a better-reducing agent below 710K, whereas CO is a better-reducing agent above 710K. (b) Generally, sulphide ores are converted into oxides before reduction. (c) Silica is added to the sulphide ore of copper in the reverberatory furnace. (d) Carbon and hydrogen are not used as reducing agents at high temperatures. (e) The Vapour phase refining method is used for the purification of Ti.

31.  Write a balanced chemical equation for the reaction showing catalytic oxidation of NH3 by atmospheric oxygen.

32. Explain why the stability of oxy acids of chlorine increases in the order given below: HCIO < HCIO2 < HCIO3 < HCIO4.

33. P4O6 reacts with water according to the equation P4O6 + 6H2O → 4H3PO3. Calculate the volume of 0.1MNaOH solution required to neutralise the acid formed by dissolving 1.1g of P4O6 in H2O.

34. What happens when the bond formed between an enzyme and an inhibitor is a strong covalent bond?

35. Nitrogen in which nitrogen is in a +3 oxidation state.

36. Why does copper not replace hydrogen from acids?

37.  Why are E- values for Mn, Ni and Zn more negative than expected?

38. Although fluorine is more electronegative than oxygen, the ability of oxygen to stabilise higher oxidation states exceeds that of fluorine. Why?

39. Mention the type of compounds formed when small atoms like H, C and N get trapped inside the crystal lattice of transition metals. Also, give the physical and Chemical characteristics of these compounds.

40. While filling up electrons in the atomic orbitals, the 4s orbital is filled before the 3d orbital but reverse happens during the ionisation of the atom. Explain why?

41. Arrange the following complexes in the increasing order of conductivity of their solution: [Co(NH3)3Cl3], [Co(NH3)4Cl2]CI, [Co(NH3)6]Cl3, [Cr(NH3)5Cl]Cl2

42. A coordination compound CrCl, 4H2O precipitates silver chloride when treated with silver nitrate. The molar conductance of its solution corresponds to a total of two ions. Write the structural formula of the compound and name it.

43. Why do compounds having similar geometry have different magnetic moments?

44. CoSO4CI.5NH3 exists in two isomeric forms ‘A’ and ‘B’. Isomer ‘A’ reacts with AgNO3 to give a white precipitate, but does not react with BaCl2. Isomer ‘B’ gives a white precipitate with BaCl2 but does not react with AgNO3. Answer the following questions. (i) Identify ‘A’ and ‘B’ and write their structural formulas. (ii) Name the type of isomerism involved. (iii) Give the IUPAC name of ‘A’ and ‘B’.

45. What is the relationship between the observed colour of the complex and the wavelength of light absorbed by the complex?

46. Aryl chlorides and bromides can be easily prepared by electrophilic substitution of arenes with chlorine and bromine respectively in the presence of Lewis acid catalysts. But why does the preparation of aryl iodides require the presence of an oxidising agent?

47. Discuss the role of Lewis acids in the preparation of aryl bromides and chlorides in the dark.

48. Why is the solubility of haloalkanes in water very low?

49. Some alkyl halides undergo substitution whereas some undergo elimination reactions on treatment with bases. Discuss the structural features of alkyl halides with the help of examples which are responsible for this difference.

50. Why are aryl halides less reactive towards nucleophilic substitution reactions than alkyl halides? How can we enhance the reactivity of aryl halides?

51. What is denatured alcohol?

52. Out of 2-chloroethanol and ethanol which is more acidic and why?

53. Arrange the following compounds in increasing order of acidity and give a suitable explanation. Phenol, o-nitrophenol, o-cresol.

54. Write the mechanism of the reaction of HI with methoxybenzene.

55. Explain a process in which a biocatalyst is used in the industrial preparation of a compound known to you.

56. Write a test to differentiate between pentan-2-one and pentan-3-one.

57. Oxidation of ketones involves carbon-carbon bond cleavage. Name the products formed on oxidation of 2, 5-dimethyl hexane-3-one.

58. An aromatic compound “A’ (Molecular formula C8H8O) gives a positive 2, 4-DNP test. It gives a yellow precipitate of compound ‘B’ on treatment with iodine and sodium hydroxide solution. Compound A’ does not give Tollen’s or Fehling’s test. On severe oxidation, potassium permanganate forms a carboxylic acid ‘C’ (Molecular formula C7H602), which is also formed along with the yellow compound in the above reaction. Identify A, B and C and write all the reactions involved.

59. Write down functional isomers of a carbonyl compound with molecular formula C3H6O. Which isomer will react faster with HCN and why? Explain the mechanism of the reaction also. Will the reaction lead to the completion with the conversion of the whole reactant into product reaction conditions? If a strong acid is added to the reaction mixture, what will be the effect on the concentration of the product and why?

60. Why are carboxylic acids more acidic than alcohols or phenols, although they all have hydrogen atoms attached to an oxygen atom (-0-H)?

61. What is the role of HNO3 in the nitrating mixture used for the nitration of benzene?

62. What is the best reagent to convert nitrile to primary amine?

63. Arrange the following compounds in increasing order of dipole moment. CH3CH2CH3, CH3CH2NH2, CH3CH2OH.

64. A colourless substance ‘A’ (C6H7N) is sparingly soluble in water and gives a water-soluble compound ‘B’ on treatment with mineral acid. On reacting with CHCI3 and alcoholic potash, ‘A’ produces an obnoxious smell due to compound ‘C’ formation. The reaction of ‘A’ with benzene sulphonyl chloride gives compound ‘D’, which is soluble in alkali. With NaNO2 and HCI, ‘A’ forms compound ‘E’, which reacts with phenol in an alkaline medium to give’ F’ orange dye. Identify compounds ‘A’ to ‘F’.

65. A hydrocarbon ‘A’, (C4H8) on reaction with HCl gives a compound ‘B’, (C4H9CI), which on reaction with 1 mol of NH3 gives compound ‘C’, (C4H11N). On reacting with NaNO2 and HCI followed by treatment with water, compound ‘C’ yields optically active alcohol, ‘D’. Ozonolysis of ‘A’ gives 2 moles of acetaldehyde. Identify compounds ‘A’ to ‘D’. Explain the reactions involved.

66. Name the sugar present in milk. How many monosaccharide units are present in it? What are such oligosaccharides called?

67. A base is attached at the first position of sugar moiety in the nucleoside. A nucleotide is formed by linking the phosphoric acid unit to the sugar unit of the nucleoside. At which position of the sugar unit is the phosphoric acid linked in a nucleoside to give a nucleotide?

68.  Monosaccharides contain carbonyl groups and hence are classified as aldose or ketose. The number of carbon atoms present in the monosaccharide molecule is also considered for classification. In which class of monosaccharides will you place fructose?

69. Which sugar is called inverted sugar? Why is it called so?

70. Write the structures of fragments produced on the complete hydrolysis of DNA. How are they linked in DNA molecules? Draw a diagram to show the pairing of nucleotide bases in the double helix of DNA.

71. Can an enzyme be called a polymer?

72. Can nucleic acids, proteins and starch be considered step-growth polymers?

73. What is the structural difference between HDP and LDP? How does the structure account for different behaviour and nature, hence using a polymer?

74. Low-density polythene and high-density polythene are polymers of ethene, but there is a marked difference in their properties. Explain.

75. Which of the following polymers soften on heating and harden on cooling? What are the polymers with this property collectively called? What are the structural similarities between such polymers? Bakelite, urea-formaldehyde resin, polythene, polyvinyl, polystyrene.

76. What is the average molecular mass of drugs?

77. Which site of an enzyme is called an allosteric site?

78. Antacids and anti-allergic drugs are antihistamines, but they cannot replace each other. Explain why?

79. In what respect do prontosil and salvarsan resemble each other? Is there any resemblance between azo dye and prontosil? Explain.
80. Synthetic detergents have an advantage over usual soaps as far as cleansing power is concerned. However, the use of synthetic detergents over a long time creates environmental pollution. How can the pollution caused by synthetic detergents be minimised? Classify the detergents according to their chemical nature.

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Benefits of Solving Most Expected Questions Class 12 Chemistry

Class 12 Chemistry’s most expected questions help you prepare the best way you can for your chemistry exam. These well-crafted questions direct your attention to the most important topics where you could spend maximum time, thereby significantly increasing your chances of opting for top marks. 

Concentrating on these questions will help strengthen your conceptual understanding and speed up solving problems while minimizing anxiety on exam day. Besides, in most cases, they follow the CBSE examination pattern, helping you to work strategically. The question of mastering excellence or enhancing confidence is in your hands since these questions remain your best Chemistry-achieving ammunition. Begin today and realize what you can accomplish!

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