NIOS Class 12 Chemistry Question Paper October 2025 with All 43 Questions
The NIOS Class 12 Chemistry question paper for the October 2025 session carries code number 70/OSS/2 and subject code 313. This page reproduces the complete paper for Set A, Set B and Set C exactly as printed, covering all 43 questions in each set, along with the marking scheme, the section structure and a topic-wise breakdown of what the paper actually tested. Every question below is transcribed from the original booklet. Nothing has been paraphrased, shortened or invented.
Authored by Prateek Talwar | Reviewed by Rohit Sharma, Senior NIOS Counsellor | Last updated 14 July 2026
NIOS Class 12 Chemistry Question Paper October 2025 Overview
Chemistry (313) is a Senior Secondary subject under the National Institute of Open Schooling. The theory paper is worth 80 marks and runs for 3 hours, with 15 minutes of additional reading time. The question paper is bilingual, printed in English and Hindi, and candidates may answer in any one of the listed regional languages. In case of any ambiguity, the English version prevails.
| Detail | Value |
|---|---|
| Subject and code | Chemistry (313) |
| Question paper code | 70/OSS/2 |
| Sets released | Set A, Set B, Set C |
| Session | October 2025 [VERIFY: session month is not printed on the booklet] |
| Total questions | 43 |
| Maximum marks | 80 |
| Duration | 3 hours |
| Printed pages | 16 |
| Compulsory questions | All questions are compulsory |
Section and Marking Structure
Both sections follow a fixed pattern in every set. Only the question order changes between Set A, Set B and Set C.
- Section A, Q1 to Q16: Multiple choice questions carrying 1 mark each. Select and write the most appropriate option out of the four given.
- Section A, Q17 to Q28: Objective type questions carrying 2 marks each, with 2 sub-parts of 1 mark each.
- Section B, Q29 to Q37: Very short answer questions carrying 2 marks each, answered in 30 to 50 words.
- Section B, Q38 to Q41: Short answer questions carrying 3 marks each, answered in 50 to 80 words.
- Section B, Q42 and Q43: Long answer questions carrying 5 marks each, answered in 80 to 120 words.
- An internal choice is provided in some Section B questions. Only one option is to be attempted.
- Log tables may be used where necessary.
The mark distribution works out to 16 marks from MCQs, 24 marks from objective questions, 18 marks from very short answers, 12 marks from short answers and 10 marks from long answers.
Set A Verbatim Questions Code 70 OSS 2
Section A Multiple Choice Questions 1 to 16
1. One micrometer stands for: (A) 10−3 m (B) 10−6 m (C) 10−9 m (D) 10−12 m
2. The number of atoms present in 0.05 g of water is: (A) 1.67 × 1023 (B) 1.67 × 1022 (C) 5.02 × 1021 (D) 1.67 × 1021
3. Li exhibits diagonal relationship with: (A) Mg (B) Ca (C) Al (D) Be
4. Shape of orbital is governed by: (A) Principal quantum number (B) Azimuthal quantum number (C) Magnetic quantum number (D) Spin quantum number
5. Shape of water molecule is: (A) Tetrahedral (B) Trigonal bipyramidal (C) Bent (D) Square planar
6. An electrovalent bond is formed between: (A) Metallic and metallic elements (B) Electronegative and electronegative atoms (C) Electropositive and electropositive atoms (D) Electropositive and electronegative atoms
7. Which one of the following is insoluble in water? (A) BaSO4 (B) MgSO4 (C) CaSO4 (D) BeSO4
8. The momentum of particle having de-Broglie wavelength 0.1 nm is: (A) 6.626 × 10−21 kg ms−1 (B) 6.626 × 10−24 kg ms−1 (C) 6.626 × 1022 kg ms−1 (D) 6.626 × 10−23 kg ms−1
9. The Reagent with which both acetaldehyde and acetone react easily is: (A) Fehling solution (B) Schiff's reagent (C) Grignard's reagent (D) Tollen's reagent
10. The equilibrium Cr2O72− ⇌ 2CrO42− exist in: (A) Neutral medium (B) Basic medium (C) Acidic medium (D) Neutral and acidic medium
11. Which of the following complex species involves sp3d2 hybridization? (A) [Co(NH3)6]3+ (B) K4[Fe(CN)6] (C) K3[Fe(CN)6] (D) [CoF6]3−
12. The complexes [Cr(H2O)6]Cl3 and [Cr(H2O)4Cl2]Cl . 2H2O exhibit: (A) Linkage isomerism (B) Hydrate isomerism (C) Coordination isomerism (D) Ionization isomerism
13. The IUPAC name of (CH3)2 CHCH3 is: (A) Dimethylethane (B) Trimethylmethane (C) 2-methylpropane (D) Isopropylmethane
14. Which of the following is the most stable radical? (A) •CH3 (B) R•CH2 (C) R2•CH (D) R3•C
15. Which of the following is natural polymer? (A) Bakelite (B) Nylon (C) Protein (D) PVC
16. Isoprene is monomer of: (A) Starch (B) Natural rubber (C) Synthetic rubber (D) PVC
Section A Objective Questions 17 to 28
17. Complete the following choosing from the given options below: (25 g, 50 g, 20 g, 2.5, 0.5, 5)
(a) The mass of CaCO3 produced when carbon dioxide passed through 500 mL of 0.5 M Ca(OH)2 will be ________.
(b) The moles of O2 required for reacting with 6.8 g NH3 according to the following reaction 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(ℓ) is ________.
18. Read the passage given below and answer the following questions:
When an electric current is passed through a discharge tube containing hydrogen gas at low pressure, it emits light. When this light is passed through a prism it splits into five lines.
(i) What is difference between the line and continuous spectrum?
(ii) Name the region of spectrum in which Lyman and Paschen emission lines are observed.
19. Write True (T) for correct statement and False (F) for incorrect statement.
(a) O2+ has bond order 2.5.
(b) All the new hybrid orbitals formed are not identical in their shape and energy.
20. Complete the following choosing from the given options: (one, two, zero, 4, 2, 3)
(a) Be2 is not formed because its bond order is ________.
(b) The number of molecular orbitals formed by mixing two atomic orbitals from each of two atoms is ________.
21. Complete the following by choosing from the given options: (Lowest, Highest 5, 2, 10)
(a) The ionization enthalpy of noble gases is ________ as compared to other elements of same period.
(b) The number of water molecules of crystallization in sodium carbonate (washing soda) is ________.
22. Read the passage given below and answer the following questions:
Ozone is an allotrope of oxygen. Ozone layer depletion in the upper atmosphere is causing a great environmental concern. It acts as oxidizing agent and also form ozonides.
(a) Why ozone acts as an oxidising agent?
(b) What is ozonide?
23. Read the passage given below and answer the following questions:
A characteristic property of d-block elements is their ability to exhibit a variety of oxidation states in their compounds. This is due to the fact that for bonding, in addition to ns electrons, these elements can use inner (n−1)d electrons as well.
(a) Name the element of first transition series which does not show variable oxidation states, also mention its oxidation state.
(b) Name the element of first transition series which shows highest oxidation states. Also mention its highest oxidation state.
24. Match the items in Column I with Column II:
Column I: (i) Carbanion (ii) Free radical (iii) Electrophile (iv) Nucleophile
Column II: (a) BF3 (b) H2O (c) •CH3 (d) +CH3
25. Complete and balance the following reactions:
(a) CH ≡ CH + [O] ⟶[Alkaline KMnO4] ?
(b) CH2 = CH2 + H2O ⟶[Hot H2SO4] ?
26. Read the passage given below and answer the following questions:
In alkyl halides, carbon-halogen bond is formed by the overlap of the sp3 hybrid orbital of carbon atom with p-orbital of halogen atom. As the size of halogen atom increases, the overlap decreases. Also due to the high electronegativity of the halogen atoms, the electron density along the C – X bond is displaced in the direction of the halogen atom. Thus C – X bond become polar in nature.
(a) Which haloalkane is more reactive Iodoalkane or Fluoroalkane? Why?
(b) Give one example of Elimination reaction.
27. Write true (T) for correct statement and False (F) for incorrect statement:
(a) The structure of protein molecule is not changed by changing pH.
(b) Fats are main food storage compounds and serve as reservoir of energy.
28. Read the passage given below and answer the following questions:
Both soap and detergent molecules have two parts. One part of the molecule is polar in nature. The polar group is hydrophilic group. The other part of soap or detergent molecule is nonpolar that is lipophilic.
(a) What is the polar part in a synthetic detergent molecule?
(b) What is oil soluble part in the soap molecule?
Section B Subjective Questions 29 to 43
29. State Lavoiser - Law of thermochemistry with suitable example. [2]
OR
Define enthalpy of atomization. Give one example.
30. The enthalpies of formation of OH(g), H(g) and O(g) are 42, 218 and 248 kJ mol−1. Calculate the bond enthalpy of O-H. [2]
31. Identify the type of system shown in the figure given below. Define this system. [2]
(Figure shows Surrounding, Vapour, Liquid and Heat.)
32. What is Buffer solution? Give one example of each acidic and basic buffer. [2]
OR
What is polyprotic acid? Give any two examples of polyprotic acid.
33. At 298 K, E° of the cell Zn|Zn2+ || Cu2+ | Cu is 1.1 V. Calculate the ΔG for the reaction. [2]
OR
Calculate the E° cell for the following reaction at 298 K. Ecell = 1.98 V.
2Al(s) + 3Cu2+ (0.01 M) → 2Al3+ (0.01 M) + 3Cu(s)
34. The standard electrode potential for Deniell cell is 1.1 V. Calculate the standard Gibbs energy for the cell reaction. (F = 96500 c mol−1). [2]
OR
Explain how the molar conductivity of strong electrolyte vary with dilution of solution.
35. State Henry's law and list the conditions necessary for the validity of Henry's law. [2]
OR
Calculate the normality of NaOH if 0.4 g NaOH is dissolved in 100 mL of solution.
36. How will you obtain (a) N-phenyl hydroxylamine and (b) Azobenzene from nitrobenzene? Write chemical equations involved. [2]
37. Complete and balance the following reactions: [2]
(i) 2KMnO4 + 2KOH ⟶[Δ]
(ii) Cr2O72− + 14H+ + 6I− →
38. What is meant by Osmosis and Reverse Osmosis? Write one application of Reverse Osmosis. [3]
OR
State Raoult's law for a solution of two volatile liquids. Derive the relationship for total vapour pressure of a solution containing two volatile liquids.
39. Find the (i) boiling point and (ii) freezing point of a solution containing 0.820 g glucose (molar mass = 180 g mol−1) dissolved in 100 g of water. (Kf = 1.86 km−1 and Kb = 0.52 km−1 for water) [3]
40. Explain the method for the preparation of Salt bridge. Give its functions. In Daniell cell what is used in place of Salt bridge? [3]
OR
What is standard hydrogen electrode? How is it formed? Write reactions when it is acting as (i) anode and (ii) Cathode.
41. Derive the expression for the degree of dissociation of weak acid. What is the effect of common ion on the degree of dissociation? [3]
42. (a) Give the IUPAC names of the following: [5]
(i) [Ni (NH3)2 (H2O)2 Cl2]
(ii) [Cr (en)2 Br2]+
(b) For the complex [Rh (en)2 Cl2]+
(i) Identify the number of geometrical isomers and draw their structures.
(ii) Identify whether there are optical isomers also, if so draw their structure.
OR
Explain shapes, hybridization and magnetic behaviour of the following complexes:
[Co (NH3)6]3+ and [Cr (NH3)6]3+ [Atomic Number : Cr = 24, Co = 27]
43. (a) Give the chemical reactions for the following: [5]
(i) Cannizaro reaction
(ii) Williamson synthesis
(iii) Hofmann bromamide reaction
(b) How will you convert nitrobenzene to aniline?
(c) How will you distinguish between primary, secondary and tertiary alcohols.
OR
(a) Arrange the following in order of increasing order of acidity:
CH3COOH, ClCH2COOH, Cl2CHCOOH, Cl3CCOOH
(b) Give simple chemical test to distinguish between the following pairs of compound:
(i) Acetaldehyde and Acetone
(ii) Phenol and Benzoic acid
(c) Explain anti-Markownikoff's addition with example.
Set B Verbatim Questions Code 70 OSS 2
Section A Multiple Choice Questions 1 to 16
1. Isoprene is monomer of: (A) Starch (B) Natural rubber (C) Synthetic rubber (D) PVC
2. Which of the following is natural polymer? (A) Bakelite (B) Nylon (C) Protein (D) PVC
3. Which of the following is the most stable radical? (A) •CH3 (B) R•CH2 (C) R2•CH (D) R3•C
4. The IUPAC name of (CH3)2 CHCH3 is: (A) Dimethylethane (B) Trimethylmethane (C) 2-methylpropane (D) Isopropylmethane
5. The complexes [Cr(H2O)6]Cl3 and [Cr(H2O)4Cl2]Cl . 2H2O exhibit: (A) Linkage isomerism (B) Hydrate isomerism (C) Coordination isomerism (D) Ionization isomerism
6. Which of the following complex species involves sp3d2 hybridization? (A) [Co(NH3)6]3+ (B) K4[Fe(CN)6] (C) K3[Fe(CN)6] (D) [CoF6]3−
7. The equilibrium Cr2O72− ⇌ 2CrO42− exist in: (A) Neutral medium (B) Basic medium (C) Acidic medium (D) Neutral and acidic medium
8. The Reagent with which both acetaldehyde and acetone react easily is: (A) Fehling solution (B) Schiff's reagent (C) Grignard's reagent (D) Tollen's reagent
9. The momentum of particle having de-Broglie wavelength 0.1 nm is: (A) 6.626 × 10−21 kg ms−1 (B) 6.626 × 10−24 kg ms−1 (C) 6.626 × 1022 kg ms−1 (D) 6.626 × 10−23 kg ms−1
10. Which of the following is the strongest base? (A) Be(OH)2 (B) Mg(OH)2 (C) Ca(OH)2 (D) Ba(OH)2
11. A covalent bond is formed between: (A) Electronegative and electronegative atoms (B) Electropositive and electropositive atoms (C) Electronegative and electropositive atoms (D) Metallic and non-metallic elements
12. Shape of water molecule is: (A) Tetrahedral (B) Trigonal bipyramidal (C) Bent (D) Square planar
13. Shape of orbital is governed by: (A) Principal quantum number (B) Azimuthal quantum number (C) Magnetic quantum number (D) Spin quantum number
14. Be exhibits diagonal relationship with: (A) Mg (B) Ca (C) Al (D) B
15. The number of atoms present in 0.05 g of water is: (A) 1.67 × 1023 (B) 1.67 × 1022 (C) 5.02 × 1021 (D) 1.67 × 1021
16. One Mega meter stands for: (A) 10−6 m (B) 106 m (C) 10−3 m (D) 103 m
Section A Objective Questions 17 to 28
17. Read the passage given below and answer the following questions:
In alkyl halides, carbon-halogen bond is formed by the overlap of the sp3 hybrid orbital of carbon atom with p-orbital of halogen atom. As the size of halogen atom increases, the overlap decreases. Also due to the high electronegativity of the halogen atoms, the electron density along the C – X bond is displaced in the direction of the halogen atom. Thus C – X bond become polar in nature.
(a) Which haloalkane is more reactive Iodoalkane or Fluoroalkane? Why?
(b) Give one example of Elimination reaction.
18. Write true (T) for correct statement and False (F) for incorrect statement:
(a) The structure of protein molecule is not changed by changing pH.
(b) Fats are main food storage compounds and serve as reservoir of energy.
19. Read the passage given below and answer the following questions:
Both soap and detergent molecules have two parts. One part of the molecule is polar in nature. The polar group is hydrophilic group. The other part of soap or detergent molecule is nonpolar that is lipophilic.
(a) What is the polar part in a synthetic detergent molecule?
(b) What is oil soluble part in the soap molecule?
20. Complete and balance the following reactions:
(a) CH ≡ CH + [O] ⟶[Alkaline KMnO4] ?
(b) CH2 = CH2 + H2O ⟶[Hot H2SO4] ?
21. Match the items in Column I with Column II:
Column I: (i) Carbocation (ii) +I effect (iii) Nucleophile (iv) Free radicals
Column II: (a) NO2− (b) •CH3 (c) –CH3 (d) CH3CH2+
22. Read the passage given below and answer the following questions:
A characteristic property of d-block elements is their ability to exhibit a variety of oxidation states in their compounds. This is due to the fact that for bonding, in addition to ns electrons, these elements can use inner (n−1)d electrons as well.
(a) Name the element of first transition series which does not show variable oxidation states, also mention its oxidation state.
(b) Name the element of first transition series which shows highest oxidation states. Also mention its highest oxidation state.
23. Read the passage given below and answer the following questions:
Ozone is an allotrope of oxygen. Ozone layer depletion in the upper atmosphere is causing a great environmental concern. It acts as oxidizing agent and also form ozonides.
(a) Why ozone acts as an oxidising agent?
(b) What is ozonide?
24. Complete the following by choosing from the given options: (Acidic, Basic, Amphoteric, higher, lower, equal)
(a) Al2O3 is ________ oxide.
(b) The electronegativity of F2 is ________ than Cl2.
25. Complete the following choosing from the given options: (one, two, zero, 4, 2, 3)
(a) Be2 is not formed because its bond order is ________.
(b) The number of molecular orbitals formed by mixing two atomic orbitals from each of two atoms is ________.
26. Write True (T) for correct statement and False (F) for incorrect statement.
(a) Bond order of O2− molecule is 2.
(b) Resonance hybrid of carbonate ion has 3 contributing canonical structures.
27. Complete the following choosing from the given options below: (10, 8, 12, 1.99 × 10−21 g, 1.99 × 10−22 g, 1.99 × 10−23 g)
(a) A sample of gaseous substance weighing 0.5 g occupies a volume of 1.135 litre under STP conditions. Molar mass of substance will be ________ g mol−1.
(b) Mass of 1 atom of carbon will be ________ g.
28. Read the passage given below and answer the following questions:
When an electric current is passed through a discharge tube containing hydrogen gas at low pressure, it emits light. When this light is passed through a prism it splits into five lines.
(i) What is difference between the line and continuous spectrum?
(ii) Name the region of spectrum in which Lyman and Paschen emission lines are observed.
Section B Subjective Questions 29 to 43
29. State Henry's law and list the conditions necessary for the validity of Henry's law. [2]
OR
Calculate the normality of NaOH if 0.4 g NaOH is dissolved in 100 mL of solution.
30. At 298 K, E° of the cell Zn|Zn2+ || Cu2+ | Cu is 1.1 V. Calculate the ΔG for the reaction. [2]
OR
Calculate the E° cell for the following reaction at 298 K. Ecell = 1.98 V.
2Al(s) + 3Cu2+ (0.01 M) → 2Al3+ (0.01 M) + 3Cu(s)
31. The standard electrode potential for Deniell cell is 1.1 V. Calculate the standard Gibbs energy for the cell reaction. (F = 96500 c mol−1). [2]
OR
Explain how the molar conductivity of strong electrolyte vary with dilution of solution.
32. How will you obtain (a) N-phenyl hydroxylamine and (b) Azobenzene from nitrobenzene? Write chemical equations involved. [2]
33. Complete and balance the following reactions: [2]
(i) 2KMnO4 + 2KOH ⟶[Δ]
(ii) Cr2O72− + 14H+ + 6I− →
34. The enthalpies of formation of OH(g), H(g) and O(g) are 42, 218 and 248 kJ mol−1. Calculate the bond enthalpy of O-H. [2]
35. Identify the type of system shown in the figure given below. Define this system. [2]
(Figure shows Surrounding, Vapour, Liquid and Heat.)
36. State Lavoiser - Law of thermochemistry with suitable example. [2]
OR
Define enthalpy of atomization. Give one example.
37. What is Buffer solution? Give one example of each acidic and basic buffer. [2]
OR
What is polyprotic acid? Give any two examples of polyprotic acid.
38. Explain the method for the preparation of Salt bridge. Give its functions. In Daniell cell what is used in place of Salt bridge? [3]
OR
What is standard hydrogen electrode? How is it formed? Write reactions when it is acting as (i) anode and (ii) Cathode.
39. Derive the expression for the degree of dissociation of weak acid. What is the effect of common ion on the degree of dissociation? [3]
40. Find the (i) boiling point and (ii) freezing point of a solution containing 0.820 g glucose (molar mass = 180 g mol−1) dissolved in 100 g of water. (Kf = 1.86 km−1 and Kb = 0.52 km−1 for water) [3]
41. What is meant by Osmosis and Reverse Osmosis? Write one application of Reverse Osmosis. [3]
OR
State Raoult's law for a solution of two volatile liquids. Derive the relationship for total vapour pressure of a solution containing two volatile liquids.
42. (a) Give the IUPAC names of the following: [5]
(i) [Ni (NH3)2 (H2O)2 Cl2]
(ii) [Cr (en)2 Br2]+
(b) For the complex [Rh (en)2 Cl2]+
(i) Identify the number of geometrical isomers and draw their structures.
(ii) Identify whether there are optical isomers also, if so draw their structure.
OR
Explain shapes, hybridization and magnetic behaviour of the following complexes:
[Co (NH3)6]3+ and [Cr (NH3)6]3+ [Atomic Number : Cr = 24, Co = 27]
43. (a) Give the chemical reactions for the following: [5]
(i) Cannizaro reaction
(ii) Williamson synthesis
(iii) Hofmann bromamide reaction
(b) How will you convert nitrobenzene to aniline?
(c) How will you distinguish between primary, secondary and tertiary alcohols.
OR
(a) Arrange the following in order of increasing order of acidity:
CH3COOH, ClCH2COOH, Cl2CHCOOH, Cl3CCOOH
(b) Give simple chemical test to distinguish between the following pairs of compound:
(i) Acetaldehyde and Acetone
(ii) Phenol and Benzoic acid
(c) Explain anti-Markownikoff's addition with example.
Set C Verbatim Questions Code 70 OSS 2
Section A Multiple Choice Questions 1 to 16
1. Which of the following is natural polymer? (A) Bakelite (B) Nylon (C) Protein (D) PVC
2. Isoprene is monomer of: (A) Starch (B) Natural rubber (C) Synthetic rubber (D) PVC
3. The IUPAC name of (CH3)2 CHCH3 is: (A) Dimethylethane (B) Trimethylmethane (C) 2-methylpropane (D) Isopropylmethane
4. Which of the following is the most stable radical? (A) •CH3 (B) R•CH2 (C) R2•CH (D) R3•C
5. Which of the following complex species involves sp3d2 hybridization? (A) [Co(NH3)6]3+ (B) K4[Fe(CN)6] (C) K3[Fe(CN)6] (D) [CoF6]3−
6. The complexes [Cr(H2O)6]Cl3 and [Cr(H2O)4Cl2]Cl . 2H2O exhibit: (A) Linkage isomerism (B) Hydrate isomerism (C) Coordination isomerism (D) Ionization isomerism
7. The Reagent with which both acetaldehyde and acetone react easily is: (A) Fehling solution (B) Schiff's reagent (C) Grignard's reagent (D) Tollen's reagent
8. The equilibrium Cr2O72− ⇌ 2CrO42− exist in: (A) Neutral medium (B) Basic medium (C) Acidic medium (D) Neutral and acidic medium
9. The factors increasing the covalent character of an ionic bond are: (A) Large anion and cation having large positive charge (B) Large cation and small anion (C) Large anion and cation having small positive charge (D) Large cation and large anion
10. Shape of water molecule is: (A) Tetrahedral (B) Trigonal bipyramidal (C) Bent (D) Square planar
11. Shape of orbital is governed by: (A) Principal quantum number (B) Azimuthal quantum number (C) Magnetic quantum number (D) Spin quantum number
12. Which out of the following is thermally least stable? (A) BaSO4 (B) SrSO4 (C) CaSO4 (D) BeSO4
13. The momentum of particle having de-Broglie wavelength 0.1 nm is: (A) 6.626 × 10−21 kg ms−1 (B) 6.626 × 10−24 kg ms−1 (C) 6.626 × 1022 kg ms−1 (D) 6.626 × 10−23 kg ms−1
14. The number of atoms present in 0.05 g of water is: (A) 1.67 × 1023 (B) 1.67 × 1022 (C) 5.02 × 1021 (D) 1.67 × 1021
15. One nanometer stands for: (A) 109 m (B) 10−9 m (C) 10−6 m (D) 106 m
16. Which one of the alkali metals imparts yellow colour in the Bunsen flame? (A) Li (B) K (C) Na (D) Rb
Section A Objective Questions 17 to 28
17. Write true (T) for correct statement and False (F) for incorrect statement:
(a) The structure of protein molecule is not changed by changing pH.
(b) Fats are main food storage compounds and serve as reservoir of energy.
18. Read the passage given below and answer the following questions:
Both soap and detergent molecules have two parts. One part of the molecule is polar in nature. The polar group is hydrophilic group. The other part of soap or detergent molecule is nonpolar that is lipophilic.
(a) What is the polar part in a synthetic detergent molecule?
(b) What is oil soluble part in the soap molecule?
19. Read the passage given below and answer the following questions:
In alkyl halides, carbon-halogen bond is formed by the overlap of the sp3 hybrid orbital of carbon atom with p-orbital of halogen atom. As the size of halogen atom increases, the overlap decreases. Also due to the high electronegativity of the halogen atoms, the electron density along the C – X bond is displaced in the direction of the halogen atom. Thus C – X bond become polar in nature.
(a) Which haloalkane is more reactive Iodoalkane or Fluoroalkane? Why?
(b) Give one example of Elimination reaction.
20. Match the items in Column I with Column II:
Column I: (i) Free radicals (ii) –I effect (iii) Electrophile (iv) Carbocation
Column II: (a) CH3+CHCH3 (b) BF3 (c) –OCH3 (d) •CH3
21. Complete and balance the following reactions:
(a) CH ≡ CH + [O] ⟶[Alkaline KMnO4] ?
(b) CH2 = CH2 + H2O ⟶[Hot H2SO4] ?
22. Read the passage given below and answer the following questions:
Ozone is an allotrope of oxygen. Ozone layer depletion in the upper atmosphere is causing a great environmental concern. It acts as oxidizing agent and also form ozonides.
(a) Why ozone acts as an oxidising agent?
(b) What is ozonide?
23. Complete the following from the given options: (−1, +1, 0, 2, 5, 0)
(a) Fluorine shows ________ oxidation state.
(b) Number of water of crystallization present in backing soda is ________.
24. Complete the following choosing from the given options: (one, two, zero, 4, 2, 3)
(a) Be2 is not formed because its bond order is ________.
(b) The number of molecular orbitals formed by mixing two atomic orbitals from each of two atoms is ________.
25. Complete the following choosing from the given options below: (10, 40, 60, 6.23 × 1021, 6.23 × 1022, 6.23 × 1023)
(a) The percentage of oxygen in NaOH is ________.
(b) The number of particles in one mole of substance is ________.
26. Read the passage given below and answer the following questions:
When an electric current is passed through a discharge tube containing hydrogen gas at low pressure, it emits light. When this light is passed through a prism it splits into five lines.
(i) What is difference between the line and continuous spectrum?
(ii) Name the region of spectrum in which Lyman and Paschen emission lines are observed.
27. Write True (T) for correct statement and False (F) for incorrect statement.
(a) Bond order of O22+ molecule is 3.
(b) NH3 has tetrahedral shape.
28. Read the passage given below and answer the following questions:
A characteristic property of d-block elements is their ability to exhibit a variety of oxidation states in their compounds. This is due to the fact that for bonding, in addition to ns electrons, these elements can use inner (n−1)d electrons as well.
(a) Name the element of first transition series which does not show variable oxidation states, also mention its oxidation state.
(b) Name the element of first transition series which shows highest oxidation states. Also mention its highest oxidation state.
Section B Subjective Questions 29 to 43
29. Identify the type of system shown in the figure given below. Define this system. [2]
(Figure shows Surrounding, Vapour, Liquid and Heat.)
30. State Henry's law and list the conditions necessary for the validity of Henry's law. [2]
OR
Calculate the normality of NaOH if 0.4 g NaOH is dissolved in 100 mL of solution.
31. What is Buffer solution? Give one example of each acidic and basic buffer. [2]
OR
What is polyprotic acid? Give any two examples of polyprotic acid.
32. State Lavoiser - Law of thermochemistry with suitable example. [2]
OR
Define enthalpy of atomization. Give one example.
33. The enthalpies of formation of OH(g), H(g) and O(g) are 42, 218 and 248 kJ mol−1. Calculate the bond enthalpy of O-H. [2]
34. How will you obtain (a) N-phenyl hydroxylamine and (b) Azobenzene from nitrobenzene? Write chemical equations involved. [2]
35. At 298 K, E° of the cell Zn|Zn2+ || Cu2+ | Cu is 1.1 V. Calculate the ΔG for the reaction. [2]
OR
Calculate the E° cell for the following reaction at 298 K. Ecell = 1.98 V.
2Al(s) + 3Cu2+ (0.01 M) → 2Al3+ (0.01 M) + 3Cu(s)
36. The standard electrode potential for Deniell cell is 1.1 V. Calculate the standard Gibbs energy for the cell reaction. (F = 96500 c mol−1). [2]
OR
Explain how the molar conductivity of strong electrolyte vary with dilution of solution.
37. Complete and balance the following reactions: [2]
(i) 2KMnO4 + 2KOH ⟶[Δ]
(ii) Cr2O72− + 14H+ + 6I− →
38. Derive the expression for the degree of dissociation of weak acid. What is the effect of common ion on the degree of dissociation? [3]
39. Explain the method for the preparation of Salt bridge. Give its functions. In Daniell cell what is used in place of Salt bridge? [3]
OR
What is standard hydrogen electrode? How is it formed? Write reactions when it is acting as (i) anode and (ii) Cathode.
40. What is meant by Osmosis and Reverse Osmosis? Write one application of Reverse Osmosis. [3]
OR
State Raoult's law for a solution of two volatile liquids. Derive the relationship for total vapour pressure of a solution containing two volatile liquids.
41. Find the (i) boiling point and (ii) freezing point of a solution containing 0.820 g glucose (molar mass = 180 g mol−1) dissolved in 100 g of water. (Kf = 1.86 km−1 and Kb = 0.52 km−1 for water) [3]
42. (a) Give the IUPAC names of the following: [5]
(i) [Ni (NH3)2 (H2O)2 Cl2]
(ii) [Cr (en)2 Br2]+
(b) For the complex [Rh (en)2 Cl2]+
(i) Identify the number of geometrical isomers and draw their structures.
(ii) Identify whether there are optical isomers also, if so draw their structure.
OR
Explain shapes, hybridization and magnetic behaviour of the following complexes:
[Co (NH3)6]3+ and [Cr (NH3)6]3+ [Atomic Number : Cr = 24, Co = 27]
43. (a) Give the chemical reactions for the following: [5]
(i) Cannizaro reaction
(ii) Williamson synthesis
(iii) Hofmann bromamide reaction
(b) How will you convert nitrobenzene to aniline?
(c) How will you distinguish between primary, secondary and tertiary alcohols.
OR
(a) Arrange the following in order of increasing order of acidity:
CH3COOH, ClCH2COOH, Cl2CHCOOH, Cl3CCOOH
(b) Give simple chemical test to distinguish between the following pairs of compound:
(i) Acetaldehyde and Acetone
(ii) Phenol and Benzoic acid
(c) Explain anti-Markownikoff's addition with example.
Topic Wise Analysis of the NIOS Class 12 Chemistry Question Paper
All three sets draw from the same pool of questions. The set letter changes only the sequence, not the content, which means a candidate who works through Set A has effectively covered Set B and Set C as well. What differs is a small number of substituted MCQs. Set A tests Li diagonal relationship, solubility of sulphates and the electrovalent bond definition. Set B replaces these with strongest base among alkaline earth hydroxides, the covalent bond definition, Be diagonal relationship and the megametre unit. Set C brings in covalent character of ionic bonds, thermal stability of sulphates, the nanometre unit and the flame colour of alkali metals.
The following distribution reflects what was actually asked across the paper.
| Area | Where it appears | Approximate weight |
|---|---|---|
| Atomic structure and quantum numbers | MCQs on orbital shape and de-Broglie momentum, passage on hydrogen line spectrum | 4 marks |
| Chemical bonding and molecular orbital theory | MCQs on bond type and water shape, true or false on bond order and hybrid orbitals, molecular orbital fill-ins | 7 marks |
| Mole concept and stoichiometry | Atoms in 0.05 g water, CaCO3 mass from Ca(OH)2, moles of O2 for NH3, molar mass at STP, mass of one carbon atom | 4 to 5 marks |
| s-block and p-block elements | Diagonal relationship, sulphate solubility and thermal stability, ionisation enthalpy of noble gases, washing soda, ozone passage, oxides | 5 to 6 marks |
| d-block and coordination compounds | Hybridisation, isomerism, dichromate equilibrium, d-block passage, permanganate and dichromate balancing, Q42 in full | 11 to 12 marks |
| Thermodynamics and thermochemistry | Lavoisier and Laplace law, enthalpy of atomisation, bond enthalpy of O-H, type of system from figure | 6 marks |
| Electrochemistry | Daniell cell and ΔG, Nernst calculation, molar conductivity, salt bridge, standard hydrogen electrode | 7 to 9 marks |
| Solutions and colligative properties | Henry's law, normality, osmosis and reverse osmosis, Raoult's law, boiling and freezing point of glucose solution | 8 marks |
| Ionic equilibrium | Buffer solution, polyprotic acid, degree of dissociation of weak acid and common ion effect | 5 marks |
| Organic reaction mechanism and functional groups | IUPAC naming, radical stability, reagents for carbonyl compounds, reaction intermediates matching, alkyl halide passage, alkyne and alkene reactions, nitrobenzene conversions, Q43 in full | 14 to 15 marks |
| Biomolecules and polymers | Natural polymer, isoprene, protein and fat true or false, soap and detergent passage | 4 marks |
What the Distribution Actually Tells You
Two chapters carry a disproportionate load. Coordination chemistry and organic reaction mechanisms together account for roughly a third of the paper, and both appear in the 5 mark long answer slots where an internal choice is available. Electrochemistry recurs in three separate questions across Section B, with the Daniell cell appearing twice in slightly different forms. Colligative properties supply one numerical worth 3 marks that is reliably solvable if the Kf and Kb formulae are memorised, which makes it among the safest marks on the paper.
Section A is where marks are lost quietly. The objective block from Q17 to Q28 carries 24 marks, more than any other block, yet each question is only worth 2 marks and split into two sub-parts. A candidate who guesses on option-selection questions without checking units gives away marks that require no derivation to earn.
Chapter Wise Topics Covered in Chemistry 313
The 313 syllabus is organised into modules. The topics below are those the October 2025 paper drew on directly.
- Atoms and molecules: mole concept, Avogadro number, percentage composition, molar volume at STP, empirical and molecular formula
- Atomic structure: Bohr model, hydrogen spectrum, Lyman and Balmer and Paschen series, de-Broglie relation, quantum numbers, orbital shapes
- Periodic table and periodicity: ionisation enthalpy trends, electronegativity, diagonal relationship, anomalous behaviour of Li and Be
- Chemical bonding: ionic and covalent bond formation, Fajans rules and covalent character, VSEPR and molecular shapes, hybridisation, molecular orbital theory and bond order, resonance
- States of matter and thermodynamics: open and closed and isolated systems, enthalpy of formation and atomisation, Hess law, Lavoisier and Laplace law, bond enthalpy
- Chemical equilibrium and ionic equilibrium: buffer solutions, polyprotic acids, degree of dissociation, common ion effect, dichromate and chromate equilibrium
- Solutions: normality and molarity, Henry's law, Raoult's law, elevation of boiling point, depression of freezing point, osmosis and reverse osmosis
- Electrochemistry: Daniell cell, electrode potential, Nernst equation, Gibbs energy of cell reaction, salt bridge, standard hydrogen electrode, molar conductivity and dilution
- s-block and p-block elements: alkali and alkaline earth metals, flame colours, hydroxide basicity, sulphate solubility and thermal stability, oxides, ozone, halogens
- d-block elements: variable oxidation states, permanganate and dichromate chemistry, oxidising behaviour
- Coordination compounds: IUPAC nomenclature, valence bond theory and hybridisation, geometrical and optical isomerism, hydrate and ionisation and linkage isomerism, magnetic behaviour
- Fundamentals of organic chemistry: IUPAC naming, inductive effect, carbocations and carbanions and free radicals, electrophiles and nucleophiles, stability order
- Hydrocarbons and haloalkanes: oxidation of alkynes, hydration of alkenes, Markownikoff and anti-Markownikoff addition, reactivity of haloalkanes, elimination reactions
- Alcohols and phenols and ethers: Williamson synthesis, Lucas test, distinguishing phenol from benzoic acid
- Aldehydes and ketones and carboxylic acids: Cannizzaro reaction, Fehling and Tollens and Schiff tests, acidity order of substituted acetic acids
- Nitrogen containing compounds: reduction of nitrobenzene, N-phenylhydroxylamine, azobenzene, aniline, Hofmann bromamide degradation
- Biomolecules and polymers: proteins and denaturation, fats as energy stores, soaps and detergents, natural and synthetic polymers, isoprene
How to Use This Paper for Revision
Work the paper under exam conditions before looking at any solution. Give yourself 3 hours, keep a log table beside you, and attempt every question because all 43 are compulsory. Then mark yourself against the section weights above and identify which of the eleven areas cost you the most.
The internal choices in Section B are worth planning in advance. Questions 29 and 32 through 35 and 38 and 40 and 42 and 43 all offer an alternative in Set A, and the equivalents in Set B and Set C carry the same choices. Deciding beforehand which side of each choice you will take, based on whether you are stronger at derivation or at recall, saves several minutes in the hall.
Word limits are enforced. A 2 mark answer is expected in 30 to 50 words and a 5 mark answer in 80 to 120 words. Overwriting a 2 mark answer costs time that the 5 mark questions need.
Get the Solved Version
The complete solved paper with step-by-step working for every numerical, balanced equations, drawn isomer structures and marking-scheme-aligned answers is available on request. Message the NIOS desk on WhatsApp 9654279279 and mention Chemistry 313 October 2025.
Frequently Asked Questions
What is the code number of the NIOS Class 12 Chemistry question paper for October 2025?
The code number printed on the booklet is 70/OSS/2 and the subject code is 313. The paper was issued in three sets marked A, B and C, and each set carries the same 43 questions in a different order. The set letter must be written on the answer book along with the code number, as failing to do so can affect evaluation.
How many questions are there in the NIOS Chemistry 313 paper and are all compulsory?
There are 43 questions in total and every one of them is compulsory. Section A holds 28 questions, of which 16 are multiple choice worth 1 mark each and 12 are objective questions worth 2 marks each. Section B holds 15 subjective questions. Internal choice is offered in several Section B questions, where only one alternative should be attempted.
What is the marking scheme of the NIOS Class 12 Chemistry question paper?
The paper is worth 80 marks over 3 hours. Multiple choice questions contribute 16 marks, objective questions contribute 24 marks, very short answers from Q29 to Q37 contribute 18 marks, short answers from Q38 to Q41 contribute 12 marks and the two long answers contribute 10 marks. An additional 20 marks come from practicals, assessed separately.
Do Set A, Set B and Set C of the Chemistry paper have different questions?
They are largely the same paper in a shuffled order. The subjective section is almost identical across the three sets, with only the numbering changed. A small number of multiple choice questions differ, covering alternative topics such as flame colours, thermal stability of sulphates and unit prefixes. Practising one set therefore prepares you for all three.
Are the answers to this NIOS Class 12 Chemistry question paper provided on this page?
This page reproduces the questions only, exactly as printed in the original booklet, so that candidates can attempt the paper under timed conditions without seeing solutions first. The fully solved version, with complete working, balanced equations and drawn isomer diagrams, is delivered separately through the NIOS desk on WhatsApp rather than published here. Reach the desk on 9654279279 or 9899436384.
Which topics carried the most marks in this Chemistry paper?
Organic chemistry carried the largest share at roughly 14 to 15 marks once the long answer question is counted, followed by coordination compounds and d-block chemistry at around 11 to 12 marks. Electrochemistry and solutions each contributed between 7 and 9 marks. Together these four areas accounted for well over half the total paper, which is why candidates who neglect organic chemistry rarely recover the marks elsewhere.
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