BCHCT 131 key facts: June 2026
- Course code: BCHCT-131
- Subject: Atomic Structure, Bonding, General Organic Chemistry and Aliphatic Hydrocarbons
- Programmes: Bachelor of Science (General), BSCG (first core chemistry course); also B.Sc. (Honours) Biochemistry, BSCBCH
- Credits: 4 (theory)
- Blocks and units: 4 blocks, 19 units
- Maximum marks: 50
- Duration: 2 hours
- Questions in the June 2026 paper: 14 of 5 marks each; attempt any 5 from Part A and any 5 from Part B; printed code A-1456
- Companion lab course: BCHCL-132 (2 credits)
- Paper language: printed in English and Hindi
- Sample answers on this page: 2 (Q7 and Q8); all 14 in the paid file
BCHCT 131 Solved Question Paper June 2026 answers the term-end paper of Atomic Structure, Bonding, General Organic Chemistry and Aliphatic Hydrocarbons, the first core chemistry course of the IGNOU Bachelor of Science (General), BSCG.
1. What the June 2026 Solved Paper Covers
It is our complete answer set for the official term-end paper, printed in English and Hindi across 16 pages. Our subject experts wrote an exam-length answer for each of its 14 questions after comparing it with earlier BCHCT 131 papers.
The paper swings from Dalton's postulates and a de Broglie numerical to ruthenium's configuration, MO theory for O2, the cyclopentadienyl cation, E/Z and R/S assignments, and alkene and alkyne reactions. Half the marks come from physical and inorganic ideas, half from organic chemistry.
Below you get two full sample answers, the remaining 12 questions as printed, the syllabus mapped to each block, and the topics IGNOU keeps repeating.
2. Two Answers Solved in Full, Twelve Held Back
Two questions are fully solved below, Q7 from Part A and Q8 from Part B; the other 12 questions are listed as text only and answered in the full file.
We picked these two because MO theory and aromaticity have appeared in every official BCHCT 131 paper we checked.
Paramagnetism of O2 and O22− by MO theory
Question 7: Which one is paramagnetic and why, O2 or O22−? Explain on the basis of MO theory. (5)
O2 is paramagnetic and O22− (the peroxide ion) is diamagnetic. MO theory explains this by counting the electrons each species places in the two degenerate π* antibonding orbitals.
Step 1: MO energy order. For O2 and heavier diatomics, the σ2pz orbital lies below the two π2p orbitals, so the filling order is σ1s, σ*1s, σ2s, σ*2s, σ2pz, (π2px = π2py), (π*2px = π*2py), σ*2pz.
Step 2: O2 (16 electrons). KK σ2s2 σ*2s2 σ2pz2 π2px2 π2py2 π*2px1 π*2py1. By Hund's rule, the last two electrons occupy the two degenerate π* orbitals singly with parallel spins, so O2 has two unpaired electrons.
Bond order of O2 = (Nb − Na) ÷ 2 = (10 − 6) ÷ 2 = 2, counting all 16 electrons (bonding 10, antibonding 6). Spin-only magnetic moment μ = √[n(n + 2)] = √8 ≈ 2.83 BM. This is why liquid oxygen is held between the poles of a strong magnet.
Step 3: O22− (18 electrons). KK σ2s2 σ*2s2 σ2pz2 π2px2 π2py2 π*2px2 π*2py2. The two extra electrons pair up in the π* orbitals, so every electron is paired and the ion is diamagnetic. Bond order = (10 − 8) ÷ 2 = 1, a single O-O bond as in H2O2 and Na2O2.
| Property | O2 | O22− |
|---|---|---|
| Total electrons | 16 | 18 |
| Electrons in π* orbitals | 2 (one in each) | 4 (paired) |
| Unpaired electrons | 2 | 0 |
| Bond order | 2 | 1 |
| Magnetic nature | Paramagnetic | Diamagnetic |
| Bond length (approx.) | 121 pm | 149 pm |
Conclusion. O2 is paramagnetic because two electrons sit unpaired in the degenerate π*2p orbitals. The Lewis structure O=O shows all electrons paired and cannot explain this, which is one of the strongest arguments for MO theory.
The cyclopentadienyl cation, and an IUPAC name
Question 8 (a): For the given structure of the cyclopentadienyl cation (five-membered ring with two C=C bonds; the starred carbon carries H and the positive charge), give: (4)
(i) hybridisation of the marked carbon (*)
(ii) planarity of the molecule
(iii) Hückel's rule as applied to the molecule
(iv) aromatic nature of the compoundQuestion 8 (b): Write the IUPAC name of the following compound: C6H5-CH2-CH=CH2 (1)
(a) The cyclopentadienyl cation
(i) Hybridisation of the starred carbon: sp2. The marked carbon carries the positive charge and forms three σ bonds (one C-H, two ring C-C) with no lone pair. It uses three sp2 hybrid orbitals, and its unhybridised 2p orbital stays empty, perpendicular to the ring.
(ii) Planarity: the ion is planar. All five ring carbons are sp2; four belong to the two C=C bonds and one is the carbocation. The ring angle of a regular pentagon (108°) is close to the ideal 120°, so the ring lies flat and all five p orbitals stand parallel, allowing continuous cyclic overlap.
(iii) Hückel's rule: not satisfied. A planar, cyclic, fully conjugated system is aromatic only with (4n + 2) π electrons. The two C=C bonds give 4 π electrons and the empty p orbital adds none. Since 4 = 4n with n = 1, the cation has 4n π electrons, not 4n + 2.
(iv) Aromatic nature: antiaromatic. Being cyclic, planar and conjugated with 4n π electrons, the cation is antiaromatic and far less stable than an open-chain allylic cation. In its π MO picture, two electrons fill the lowest orbital and the other two sit singly in two degenerate bonding orbitals.
That is why the cyclopentadienyl cation is highly reactive and hard to generate. Its partner, the cyclopentadienyl anion, has 6 π electrons (n = 1), is aromatic, and explains the unusual acidity of cyclopentadiene (pKa about 16).
(b) IUPAC name
3-phenylprop-1-ene (common name allylbenzene). The three-carbon chain holds the double bond at C-1 and the phenyl group at C-3. Under current IUPAC recommendations, the ring can also be taken as parent, giving (prop-2-en-1-yl)benzene.
3. Questions Answered Only in the Full File
These 12 questions appear exactly as printed in the June 2026 paper. Their answers are in the full file only.
Question 1 (Part A): What are the postulates of Dalton's atomic theory? (5)
Question 2 (Part A): (a) What is black body radiation? (2) (b) Calculate the momentum of a particle which has a de Broglie wavelength of 2.5 × 10−10 m. (h = 6.6 × 10−34 kg m2 s−1) (3)
Question 3 (Part A): Write the electronic configuration of ruthenium (Z = 44). Does it follow the Aufbau principle? Explain giving reasons. (5)
Question 4 (Part A): (a) What is electron affinity? Also give its unit. (2) (b) The electron affinity values of halogens are large and more negative. Why? (3)
Question 5 (Part A): (a) On the basis of valence bond theory predict the shapes of the following: (i) AsF5 (ii) SO42− (4) (b) Which one would be more polarisable, F− or I−? (1)
Question 6 (Part A): Write the Schrödinger equation and explain the terms appearing in it. (5)
Question 9 (Part B): (a) Suggest a method for the synthesis of any two of the following: (i) CH3-CH2-CH2-CH3 using CH3-CH2-COOH (ii) CH4 using CH3Cl (iii) cis-CH3CH=CHCH3 using CH3-C≡C-CH3 (4) (b) What are the octane numbers of iso-octane and n-heptane? (1)
Question 10 (Part B): (a) Assign E or Z configuration to any one of the following molecules, giving the priority orders of the substituents. (3) (b) Explain, giving structures, why maleic acid readily forms maleic anhydride while its trans isomer, fumaric acid, does not. (2)
Question 11 (Part B): (a) Draw the meso structure of butane-2,3-diol using a Fischer projection. Categorise it as erythro or threo. (2) (b) Explain why meso compounds are optically inactive. (1) (c) Assign R or S configuration to the given compound, assigning the priority order to the groups attached. (2)
Question 12 (Part B): (a) Suggest a method for the preparation of CH3-C(CH3)=CH-CH3 using dehydrohalogenation of an alkyl halide. (2) (b) Write the mechanism involved and the products formed when CH3-CH=CH2 reacts with Br2 in CCl4 at room temperature. Explain why it is called trans addition. (3)
Question 13 (Part B): (a) Write the products formed when CH3-C(CH3)=CH-CH3 reacts with HBr (i) without peroxide (ii) with peroxide. (2) (b) Identify A and B in the following reactions. (3)
Question 14 (Part B): (a) Give the hybridisation and draw the planar structure of the methyl radical. (1) (b) What is bond heterolysis? (1) (c) Using a Newman projection, draw the chair conformation of cyclohexane. (1) (d) Explain, on the basis of resonance, why aniline is less basic than ammonia. (2)
4. Block and Unit Wise Syllabus
BCHCT 131 has 4 blocks and 19 units: Blocks 1 and 2 cover atomic structure and bonding, while Blocks 3 and 4 cover organic fundamentals and hydrocarbons.
The unit list below comes from the official block introductions, and each row shows where this paper and earlier papers drew their questions. For the full texts, see the BCHCT-131 course page on eGyanKosh.
| Block and unit | Topics examined in official papers |
|---|---|
| Block 1: Atomic Structure, Unit 1: Bohr's Theory | Dalton's postulates (Q1, 2026); Bohr's postulates (Jun 2024); limitations of Bohr's theory (Dec 2022) |
| Block 1, Units 2 and 3 | Black body radiation (Q2a); de Broglie momentum numerical (Q2b); Heisenberg uncertainty principle (Jun 2024) |
| Block 1, Unit 4: Structure of Hydrogen Atom | Schrödinger equation and its terms (Q6); quantum numbers of 2s and 4d electrons (Dec 2023, Dec 2022) |
| Block 1, Unit 5: Electronic Configurations of Multi-electron Atoms | Ruthenium, Z = 44, and Aufbau (Q3); niobium, Z = 41 (Jun 2024); Hund's rule (Dec 2023) |
| Block 2: Chemical Bonding, Unit 6: Ionic Bond | Polarisability of F− versus I− (Q5b); lattice energy (Dec 2023); Li+ and Be2+ radii (Dec 2022) |
| Block 2, Unit 7: Covalent Bond | Lewis structure of CO2 (Jun 2024); HCN and HNO2 (Dec 2023); nitrate resonance (Dec 2022) |
| Block 2, Unit 8: Valence Bond Theory | Shapes of AsF5 and SO42− (Q5a); IF5 (Dec 2022); carbonate ion (Dec 2023) |
| Block 2, Unit 9: Molecular Orbital Theory | O2 versus O22− (Q7, Sample 1); NO versus NO+ (Dec 2023); LCAO short note (Jun 2024) |
| Block 3, Unit 10: Geometrical and Optical Isomerism | E/Z priority orders (Q10a); maleic versus fumaric acid (Q10b); dipole moment of ClCH=CHCl (Dec 2023) |
| Block 3, Unit 11: Configurational Isomers | Meso butane-2,3-diol, erythro or threo (Q11a); R/S from a Fischer projection (Q11c); tartaric acid isomers (Dec 2023) |
| Block 3, Unit 12: Conformational Isomerism | Chair cyclohexane in Newman projection (Q14c); n-butane conformers (Dec 2023); ethane (Jun 2024) |
| Block 3, Units 13 and 14 | Methyl radical shape (Q14a); bond heterolysis (Q14b); aniline versus ammonia basicity (Q14d) |
| Block 4, Unit 15: Alkanes | Butane from propanoic acid and methane from CH3Cl (Q9a); octane numbers (Q9b); chlorination of methane (Dec 2023) |
| Block 4, Units 16 and 17: Alkenes | Dehydrohalogenation route (Q12a); Br2 trans addition (Q12b); HBr with and without peroxide (Q13a) |
| Block 4, Unit 18: Alkynes | But-2-yne to cis-but-2-ene (Q9a iii); hydration of but-1-yne (Q13b iii); ethyne to 1-butyne (Dec 2023) |
| Block 4, Unit 19: Aromaticity | Cyclopentadienyl cation and Hückel's rule (Q8a, Sample 2); cyclopentadienyl anion versus cation (Dec 2022) |
Revise unit by unit from the official blocks or our BCHCT 131 Study Material, then test yourself on the matching questions. Units 9, 11 and 19 alone supplied three of this paper's 14 questions.
5. Question Paper Pattern and Marks Distribution
The June 2026 paper has 14 questions of 5 marks each; you answer 5 from Part A and 5 from Part B for 50 marks in 2 hours.
| Part | Questions printed | You attempt | Marks | Mark splits seen in June 2026 |
|---|---|---|---|---|
| Part A: atomic structure and bonding | Q1 to Q7 | Any 5 | 5 × 5 = 25 | Single 5-mark questions (Q1, Q3, Q6, Q7) and 2 + 3 or 4 + 1 splits (Q2, Q4, Q5) |
| Part B: organic chemistry and hydrocarbons | Q8 to Q14 | Any 5 | 5 × 5 = 25 | 4 + 1 (Q8, Q9), 3 + 2 (Q10), 2 + 1 + 2 (Q11), 2 + 3 (Q12, Q13), 1 + 1 + 1 + 2 (Q14) |
Each part goes on a separate answer sheet, so label both sheets clearly. Part B leans on drawing: Fischer projections, Newman projections and reaction mechanisms, where a clean structure matters as much as the text.
Older papers used the same two-part, 25 + 25 layout, so practice on any recent BSCG Question Paper carries straight over to this one.
6. Most Repeated Topics Across Official Papers
Eleven topic areas appeared in all four official BCHCT 131 papers we checked: December 2022, December 2023, June 2024 and June 2026.
| Topic | How it was asked | Papers (of 4) |
|---|---|---|
| Electronic configuration and Aufbau exceptions | La and Sr (Dec 2022); Fe3+ (Dec 2023); Nb (Jun 2024); Ru (Jun 2026) | 4 |
| MO theory: magnetism and bond order | O2 bond order (Dec 2022); NO and NO+ (Dec 2023); LCAO (Jun 2024); O2 and O22− (Jun 2026, Sample 1) | 4 |
| Schrödinger equation and wave function | Well-behaved wave function (Dec 2022); applying the equation (Dec 2023, Jun 2024); terms of the equation (Jun 2026) | 4 |
| Ionisation energy and electron affinity | Li+ versus Ne+ (Dec 2022); Na, K, Li order (Dec 2023); O versus N (Jun 2024); halogen electron affinity (Jun 2026) | 4 |
| Resonance structures | Nitrate ion (Dec 2022, Jun 2024); cyanate ion and aniline (Dec 2023); aniline basicity (Jun 2026) | 4 |
| Aromaticity and Hückel's rule | Cyclopentadienyl ions (Dec 2022); aromatic or not (Dec 2023); classify compounds (Jun 2024); cyclopentadienyl cation (Jun 2026, Sample 2) | 4 |
| Optical isomerism, R/S and meso forms | Tartaric acid Fischer projections (Dec 2022, Dec 2023); R/S rules (Jun 2024); meso diol and R/S (Jun 2026) | 4 |
| Conformations and Newman projections | Chair versus boat (Dec 2022); n-butane (Dec 2023); ethane (Jun 2024); chair cyclohexane (Jun 2026) | 4 |
| HBr addition and peroxide effect | Propene (Dec 2022, Jun 2024); Markownikoff's rule (Dec 2023); 2-methylbut-2-ene (Jun 2026) | 4 |
| Alkyne reactions | Ozonolysis of but-2-yne (Dec 2022); ethyne conversions (Dec 2023); hydration and Na/NH3 (Jun 2024); partial reduction and hydration (Jun 2026) | 4 |
| Acid and base strength | Brønsted acids (Dec 2022); acid strength order (Dec 2023); chloroacetic acids and nucleophilicity (Jun 2024); aniline versus ammonia (Jun 2026) | 4 |
| VSEPR and VBT shapes | IF5 (Dec 2022); carbonate ion (Dec 2023); AsF5 and SO42− (Jun 2026) | 3 |
| E/Z configuration | Single compound (Dec 2022); two compounds (Dec 2023); priority orders (Jun 2026) | 3 |
| Carbocations and radicals | Carbocation stability order (Dec 2022, Dec 2023); methyl radical shape (Jun 2026) | 3 |
| Ozonolysis | But-2-yne (Dec 2022); alkene giving acetone (Dec 2023); alkene giving 2CH3CHO (Jun 2026) | 3 |
| Quantum numbers | 4d electron (Dec 2022); 2s electrons (Dec 2023); types and significance (Jun 2024) | 3 |
| Dalton's atomic theory | Five postulates (Dec 2023); postulates (Jun 2026) | 2 |
| de Broglie relation numericals | Wavelength of a 2.2 × 10−2 kg object (Dec 2023); momentum from wavelength (Jun 2026) | 2 |
We counted only papers we could open on IGNOU's own question paper server. The June 2023, December 2024, June 2025 and December 2025 papers were not available to us there, so this table does not claim a five-year run.
The pattern is clear: IGNOU swaps the example, not the idea. Ruthenium replaced niobium, and the peroxide ion replaced NO. For more course-wise lists, see our IGNOU Solved Guess Paper page.
7. How Our Answers Are Written and Checked
Every BCHCT 131 answer is written to the mark value printed against it, with structures, equations and units in the form IGNOU examiners expect.
A 1-mark part gets a precise statement; a 5-mark question gets a worked answer with a conclusion. Numericals show the formula, substitution and final value with SI units, and stereochemistry answers show the priority order before the E, Z, R or S label.
Our writers study each question against earlier papers, so an answer stresses what the examiner has asked before. You can compare the style with any official IGNOU Previous Year Question Paper for this course.
8. Solved File Index: All 14 Questions Mapped to Units
BCHCT 131 is a theory course, so this index maps every question in the solved file to its block and unit and shows where each answer is available.
Its laboratory work sits in the separate 2-credit lab course BCHCL-132, which has its own assessment, so no practical record is part of this paper.
| Question | Part | Topic | Block and unit | Where the answer is |
|---|---|---|---|---|
| Q1 | A | Dalton's atomic theory | Block 1, Unit 1 | Full file |
| Q2 | A | Black body radiation; de Broglie momentum | Block 1 | Full file |
| Q3 | A | Ruthenium configuration and Aufbau | Block 1, Unit 5 | Full file |
| Q4 | A | Electron affinity of halogens | Blocks 1 and 2 | Full file |
| Q5 | A | VBT shapes; polarisability | Block 2, Units 6 and 8 | Full file |
| Q6 | A | Schrödinger equation | Block 1 | Full file |
| Q7 | A | O2 versus O22− by MO theory | Block 2, Unit 9 | Sample 1 above |
| Q8 | B | Cyclopentadienyl cation; IUPAC name | Blocks 3 and 4, Unit 19 | Sample 2 above |
| Q9 | B | Alkane and alkene synthesis; octane numbers | Block 4, Units 15 and 18 | Full file |
| Q10 | B | E/Z configuration; maleic anhydride | Block 3, Unit 10 | Full file |
| Q11 | B | Meso diol; R/S assignment | Block 3, Units 10 and 11 | Full file |
| Q12 | B | Dehydrohalogenation; Br2 trans addition | Block 4, Units 16 and 17 | Full file |
| Q13 | B | HBr addition; A and B identification | Block 4, Units 16 to 18 | Full file |
| Q14 | B | Methyl radical; heterolysis; chair; aniline | Block 3 | Full file |
9. Programmes That Include BCHCT 131
BCHCT 131 is studied in two IGNOU programmes: BSCG and BSCBCH.
In the Bachelor of Science (General) programme (BSCG), BCHCT 131 is the first core chemistry course, paired with the lab course BCHCL-132. Students who pick chemistry meet it early, so it sets the base for later chemistry courses such as BCHCT-133.
In the Bachelor of Science (Honours) Biochemistry (BSCBCH), the same course supplies the bonding, stereochemistry and reactivity ideas that biochemistry keeps returning to, from chiral amino acids like the one in Q11(c) to resonance in aromatic rings.
10. How to Get the Full Solved Question Paper
Message 9899436384 on WhatsApp with "BCHCT 131 June 2026" to get the complete file with answers to all 14 questions.
You already have 2 answers on this page. The full file adds the other 12, including the ruthenium configuration, the de Broglie numerical, the Schrödinger equation, E/Z and R/S assignments and every alkene and alkyne reaction in Part B.
Our team replies with the price and delivery details. Keep your programme code handy, BSCG or BSCBCH, so we can confirm you have the right course.
11. BCHCT 131 FAQs
These answers cover the BCHCT 131 questions students ask us most before the term-end exam.
How do I get the full solved paper on WhatsApp?
Send a WhatsApp message to 9899436384 with the words BCHCT 131 June 2026. Our team replies with the price and delivery details. The full file answers all 14 questions from Part A and Part B, so you get the 12 answers not shown on this page plus the two sample answers on MO theory and the cyclopentadienyl cation in one PDF.
Which June 2026 questions are fully solved on this page?
Two questions are fully solved here. Question 7 compares O2 and O22− using molecular orbital theory, with configurations, bond order and unpaired electrons. Question 8 covers the cyclopentadienyl cation: hybridisation of the starred carbon, planarity, Hückel's rule and its antiaromatic nature, plus the IUPAC name of allylbenzene. The other 12 questions are listed as text only.
How many questions must I attempt in the BCHCT 131 exam?
You attempt ten questions in all. The paper prints seven questions in Part A on atomic structure and bonding, and seven in Part B on organic chemistry and hydrocarbons. You answer any five from each part on separate answer sheets. Every question carries 5 marks, so each part is worth 25 marks and the paper totals 50 marks in 2 hours.
Which BCHCT 131 topics repeat most often in IGNOU papers?
Eleven topic areas appeared in all four official papers we checked: December 2022, December 2023, June 2024 and June 2026. The safest are electronic configuration with Aufbau exceptions, molecular orbital theory, aromaticity, stereochemistry, conformations and HBr addition to alkenes. Dalton's postulates and de Broglie numericals each appeared twice, including this June 2026 paper, so revise them as well.
Is BCHCT 131 a practical course?
No, BCHCT 131 is a 4-credit theory course with a 50-mark term-end paper. Its laboratory work sits in a separate 2-credit lab course, BCHCL-132, which is assessed on its own. Theory questions still ask you to draw Fischer projections, Newman projections and MO diagrams, so neat labelled drawings earn marks in this written paper. Prepare for BCHCL-132 separately for its own lab assessment.
Which programmes include BCHCT 131?
BCHCT 131 is the first core chemistry course of the IGNOU Bachelor of Science (General), programme code BSCG. It is also studied in the Bachelor of Science (Honours) Biochemistry, programme code BSCBCH, where it builds the chemistry base for later biochemistry courses. The same term-end paper is set for both programmes, so this solved file suits students of either one.
How should I split my time in the 2-hour paper?
Plan about ten minutes for each of the ten questions you attempt, which leaves around 20 minutes for reading the paper and checking. Start with the part you know better. Keep numericals such as the de Broglie question short, and spend saved time on drawings like Fischer and Newman projections, where a missing label can cost you a mark.
Can the June 2026 paper help me prepare for December 2026?
Yes. Many BCHCT 131 questions return with a new example rather than a new idea. Ruthenium in 2026 followed niobium in 2024 for the Aufbau exception, and the cyclopentadienyl ions appeared in both December 2022 and June 2026. Solving this paper trains you on the formats IGNOU reuses, which is the fastest way to prepare for December 2026.
12. Who Wrote and Checked the BCHCT 131 Answers
The BCHCT 131 answers were written by Prateek Talwar and reviewed by Sheetal Kirola.
Prateek Talwar, founder of Unnati Educations, leads the IGNOU science solved-paper series and prepares answers from the course blocks and the official term-end paper. Sheetal Kirola, Academic Head (M.Ed.), checks every structure, equation and unit against the block books before release.