Coordination Compounds JEE Main PYQ — CFSE, Isomer Counting & the NVQs That Decide It (2015-2026)
Coordination Compounds JEE Main PYQ (2015-2026), 276 questions decoded. The CFSE table, the Ni-trio trap, isomer-counting NVQs, mnemonics, and 15 PYQs with solutions.
This Is the Highest-ROI Inorganic Chapter — Because It's Rules, Not Rote.
Most of JEE Main Inorganic is memorisation — p-block anomalies, decomposition trends, reaction after reaction. Coordination Compounds is the exception, and that's exactly why it's the highest-ROI chapter in the section: it's entirely rule-based and algorithmic. Master the spectrochemical series and the geometric rules of Crystal Field Theory, and you've unlocked over 80% of the chapter.
It carries 8-12% of the Chemistry paper, 2-3 questions per shift, and after the 2024 deletions gutted the rote-heavy Inorganic chapters, its weight only climbed. But here's what separates JEE from NEET: while NEET asks "is this complex paramagnetic," JEE makes you calculate. Compute the exact CFSE. Count the total optical isomers. Sum the unpaired electrons across five complexes at once. Deduce the coordination sphere from an AgCl precipitate mass or a freezing-point depression. Since 2025 all 5 NVQs are compulsory with −1 marking, so these calculation-heavy integer questions can't be skipped.
We analysed 276 Coordination Compounds questions across every JEE Main shift from 2015 to 2026. This is Logic Bloom's seventh JEE Main PYQ analysis, after Modern Physics, Electrodynamics, Mechanics, Chemical Bonding, Thermodynamics, and GOC.
| 🎯 We analyzed all 276 JEE Main Coordination Compounds questions. The app has them all — ready to play and practice. | |
|---|---|
| This chapter is spatial and calculation-driven — you master it by filling d-orbitals, building isomers, and computing CFSE, not by re-reading. Logic Bloom's Playground turns it into interactive practice: fill t₂g/eg and watch the CFSE and magnetic moment compute themselves, rotate a complex to count its optical isomers, run the Ni-trio side by side to see why one is square planar and one tetrahedral. Then drill every PYQ including the NVQ type. When a CFSE pairing-energy slip or a tetrahedral-low-spin error catches you, TarQ teaches the fix, and your Mistake Book logs it. | Get the app → Free to start. |
Sub-Topic Frequency: Isomerism, VBT and Magnetism Lead
| Rank | Sub-topic | Share (of 276) | Priority |
|---|---|---|---|
| 1 | Stereoisomerism (geometrical + optical) | 13.8% | Very High |
| 2 | Valence Bond Theory (hybridisation, inner/outer) | 13.0% | Very High |
| 3 | Werner's theory, coordination number, IUPAC | 12.3% | High |
| 4 | Magnetic moment (spin-only, counting) | 11.6% | High |
| 5 | Ligands (denticity, ambidentate, chelating) | 10.1% | High |
| 6 | Structural isomerism (ionisation, hydrate) | 8.0% | Moderate |
| 7 | Spectrochemical series & spin rules | 7.3% | Moderate |
| 8 | CFT splitting (Δo / Δt) | 6.5% | Moderate |
| 9 | CFSE calculation (numerical) | 5.8% | Rising fast |
| 10 | Colour & d-d transitions | 5.1% | Moderate |
The top four categories all reward calculation or spatial reasoning — not memorised facts. And CFSE calculation, though only 5.8% historically, has seen a near-300% rise in frequency since 2021. The exam is getting more numerical, not less.
The Format That Raised the Stakes: 35% NVQs, Aggressively Rising
| Format | Share | Dominant Themes |
|---|---|---|
| Numerical Value (NVQ) | ~35% | Isomer enumeration, aggregated electron counting, CFSE derivation, stoichiometric valency deduction |
| Single-correct / Match MCQ | ~65% | Δo ordering, paramagnetic selection, IUPAC, CFT statement evaluation |
The NVQ shift is what makes this chapter genuinely hard now. Instead of one isolated complex, you count total isomers for a formula, sum unpaired electrons across four or five species, derive an exact CFSE coefficient, or back-calculate the coordination sphere from an AgCl mass. Partial knowledge earns nothing, and −1 punishes the guess. This is the JEE-vs-NEET divide in one word: enumeration.
| 🎯 [NiCl₄]²⁻, [Ni(CN)₄]²⁻, [Ni(CO)₄] — three nickel complexes, three different answers. This trio is tested relentlessly. | |
|---|---|
| The Ni-trio trap. Same metal, three outcomes: [NiCl₄]²⁻ — Ni(II), weak-field Cl⁻ → sp³ tetrahedral, paramagnetic (n=2). [Ni(CN)₄]²⁻ — Ni(II), strong-field CN⁻ → dsp² square planar, diamagnetic. [Ni(CO)₄] — Ni(0), CO forces d¹⁰ → sp³ tetrahedral, diamagnetic. The killer detail: students see CO is strong-field and mark [Ni(CO)₄] square planar. But a d¹⁰ system has NO empty inner d-orbital, so it can only be sp³ tetrahedral. Strong-field doesn't always mean square planar — the d-count decides. Logic Bloom's Playground runs the three side by side so you see the orbitals fill differently — with TarQ explaining the d¹⁰ constraint. Then drill every PYQ and let your Mistake Book catch the geometry slips. | Run the Ni-trio → Free to start. |
The CFSE Table — The JEE-vs-NEET Difference, Quantified
NEET asks whether a complex is paramagnetic. JEE makes you calculate its stabilisation energy. CFSE = (−0.4·nt₂g + 0.6·neg)Δo + mP, where m = extra pairs formed relative to the high-spin state. Memorise the outputs:
| 🎯 Octahedral CFSE (d¹–d¹⁰) | ||
|---|---|---|
| d-count | High Spin (weak field) | Low Spin (strong field) |
| d¹ | −0.4 Δo | −0.4 Δo |
| d² | −0.8 Δo | −0.8 Δo |
| d³ | −1.2 Δo | −1.2 Δo |
| d⁴ | −0.6 Δo | −1.6 Δo + P |
| d⁵ | 0.0 Δo | −2.0 Δo + 2P |
| d⁶ | −0.4 Δo | −2.4 Δo + 2P |
| d⁷ | −0.8 Δo | −1.8 Δo + P |
| d⁸ | −1.2 Δo | −1.2 Δo |
| d⁹ | −0.6 Δo | −0.6 Δo |
| d¹⁰ | 0.0 Δo | 0.0 Δo |
The pairing-energy trap: for a low-spin d⁶ complex, students write −2.4Δo and stop. When Δo ≫ P (as the question usually states), the ratio comparison ignores P and −2.4Δo/−1.2Δo = 2 (the exact 2026 CFSE-ratio question). But when P matters, forgetting the +2P term is a guaranteed wrong answer. Read whether the question says "assume Δo ≫ P."
The Magnetic-Moment Table
| 🎯 Unpaired Electrons → Spin-Only Moment (μ = √n(n+2)) | |
|---|---|
| n = 1 | 1.73 BM |
| n = 2 | 2.83 BM |
| n = 3 | 3.87 BM |
| n = 4 | 4.90 BM |
| n = 5 | 5.92 BM |
The integer before the decimal always equals n — a free check under NVQ pressure. And beware "μ > 3.0 BM": since √15 = 3.87, that means n ≥ 3, so n = 3 qualifies (a 2026 trap that caught students who read it as n > 3).
Mnemonics — Make This Chapter Stick
This chapter rewards fast recall of series, rules, and constants. These memory devices are engineered to bypass cognitive overload in the exam.
| 🧠 Memory Aids for Coordination Compounds | |
|---|---|
| Spectrochemical series (weak → strong) | "If I Bring Some Clean Nickels, Friday Our Ox Water Needs Extra Ammonia In New Cyanide Cabs." I⁻ · Br⁻ · S²⁻/SCN⁻ · Cl⁻ · NO₃⁻ · F⁻ · OH⁻ · Oxalate · H₂O · NCS⁻ · EDTA · NH₃ · en · NO₂⁻ · CN⁻ · CO. (Caveat: a few middle ligands shift between textbook versions — the extremes, halides weakest and CN⁻/CO strongest, are what NTA tests hardest.) |
| Strong vs weak field, fast | "Carbon and Nitrogen pair them tight; Oxygen and Halogens keep them bright." C/N-donors (CN⁻, CO, en, NH₃) are strong-field → pairing → low spin. O/halogen-donors (H₂O, OH⁻, F⁻, Cl⁻) are weak-field → high spin. |
| Magnetic moment values | "The integer mirrors the unpaired." n = 1→1.73, 2→2.83, 3→3.87, 4→4.90, 5→5.92. The whole-number part always equals n. |
| Optical activity | "Cis stays chiral, trans is trash (achiral)." For [M(en)₂X₂]: cis is optically active, trans has a plane of symmetry. And [M(en)₃] is always chiral. |
| IUPAC naming order | "L-M-O: Ligands, Metal, Oxidation." Ligands alphabetical (ignore di/tri prefixes) → metal (add "-ate" if anionic) → oxidation state in Roman numerals. |
| Ambidentate donor atom | "Swap the front." SCN = S-donor (thiocyanato); NCS = N-donor (isothiocyanato). NO₂ = N-donor (nitrito-N); ONO = O-donor (nitrito-O). The leading atom is the donor. |
The Signature Traps
| 📌 Where Candidates Lose Marks (−1 Each Under NVQ) | |
|---|---|
| CFSE pairing-energy omission | Writing −2.4Δo for low-spin d⁶ and forgetting the +2P term when the question requires it. Always check for "assume Δo ≫ P." |
| Tetrahedral marked low spin | Δₜ = (4/9)Δo is almost always < pairing energy, so tetrahedral complexes are overwhelmingly high spin — regardless of ligand strength. |
| The trans-optical-activity error | Assuming trans isomers can be chiral. trans-[M(en)₂X₂] has a plane of symmetry → achiral. Only cis is optically active. |
| The d¹⁰ geometry slip | Marking [Ni(CO)₄] square planar because CO is strong-field. d¹⁰ has no empty inner d-orbital → only sp³ tetrahedral. |
| Ambidentate nomenclature reversal | Confusing nitrito-N (NO₂) with nitrito-O (ONO), or thiocyanato-S with isothiocyanato-N. The leading atom names the donor. |
Cross-Chapter Integration (the Real Difficulty)
| Combination | What It Tests |
|---|---|
| Coordination + d-Block | Identify the metal from highest atomisation enthalpy or E°(M³⁺/M²⁺) BEFORE you can apply CFT. A common two-step opener. |
| Coordination + Chemical Bonding | Lone-pair count on BrF₅ used as an algebraic variable to fix the isomer count. Two chapters, one integer. |
| Coordination + Mole Concept | AgCl precipitate mass or freezing-point depression (van 't Hoff factor) to deduce the coordination sphere. Highly recurrent. |
| Coordination + Stereochemistry (GOC) | Optical-isomer counting reuses the same chirality/symmetry logic as organic stereochemistry. |
JEE Main 2027 / 2028 Predictions
Predictions exclude deleted topics (biological importance, qualitative analysis, metal extraction).
Top 5 Sub-Topics Most Likely to Appear
| # | Predicted Topic | Why |
|---|---|---|
| 1 | Advanced isomer enumeration (NVQ) | Sum of geometrical + optical isomers for multi-bidentate systems. |
| 2 | Quantitative CFSE (NVQ) | Algebraic manipulation of Δo and P — the fastest-rising theme. |
| 3 | Magnetic-moment aggregation (NVQ) | Sum unpaired electrons across 4-5 mixed-field complexes. |
| 4 | Coordination-sphere stoichiometry | Molar mass → AgCl precipitate → primary/secondary valency. |
| 5 | Synergic bonding in carbonyls | C-O bond order inverse to M-C back-donation vs metal oxidation state. |
2 Dormant Concepts Due for Return
| Concept | Likely Format |
|---|---|
| EAN rule | Under-tested since 2021 — primed for a carbonyl matching-list MCQ (EAN = Z − OS + 2×CN reaching a noble-gas count). |
| Jahn-Teller distortion | A d⁹ Cu(II) discriminator — asymmetric eg filling → elongated octahedron. |
Coordination Compounds JEE Main PYQs — 15 Questions You Must Attempt
These 15 span 2015-2026 and reflect JEE's exact difficulty and NVQ style. Each has a worked one-line solution and the trap explained.
| 📌 15 Must-Attempt JEE Main Coordination Compounds PYQs | |
|---|---|
| 1. Isomer Sum (2026 Jan 28, NVQ) | X = geometrical isomers of [Pt(NH₃)(H₂O)BrCl]; Y = optically inactive isomers of [CrCl₂(ox)₂]³⁻; Z = geometrical isomers of [Co(NH₃)₃(NO₂)₃]. Find X+Y+Z. Answer: 6. Solution: Square planar MABCD → 3; the ox-complex has 1 inactive (trans) → 1; MA₃B₃ → fac + mer → 2. Total 3+1+2=6. Trap: Forgetting square-planar MABCD gives exactly 3. |
| 2. Hydrate Stoichiometry (2026 Apr 2, NVQ) | 5.33 g CrCl₃·6H₂O (1:3 electrolyte) → eluted Cl⁻ gives 8.61 g AgCl. Ratio of moles complex : AgCl (×10⁻²)? Answer: 33. Solution: 1:3 electrolyte = [Cr(H₂O)₆]Cl₃. Complex = 5.33/266.5 = 0.02; AgCl = 8.61/143.5 = 0.06; ratio 1/3 = 33×10⁻². Trap: Placing Cl⁻ inside the sphere. |
| 3. Ni-Trio Match (2025 Apr 8) | Match shape + moment: [Ni(CO)₄], [Ni(CN)₄]²⁻, [NiCl₄]²⁻, [MnBr₄]²⁻. Answer: Tetrahedral 0 BM / square planar 0 BM / tetrahedral 2.8 BM / tetrahedral 5.9 BM. Solution: Ni(0) d¹⁰ sp³; Ni(II) SFL dsp²; Ni(II) WFL sp³ n=2; Mn(II) WFL sp³ n=5. Trap: Marking [Ni(CO)₄] square planar — d¹⁰ can't be. |
| 4. Yellow Low-Spin Sum (2025 Jan 29, NVQ) | Sum of spin-only moments of the yellow complexes among K₃[Co(NO₂)₆], K₄[Fe(CN)₆], K₃[Fe(CN)₆]? Answer: 0. Solution: The two yellow ones are both d⁶ low-spin (n=0) → 0+0 = 0. Trap: Including red K₃[Fe(CN)₆] (n=1). |
| 5. CFSE Ratio (2026 Jan 23, NVQ) | CFSE of [Co(ox)₃]³⁻ is n times that of [Cr(ox)₃]³⁻ (Δo ≫ P). Find n. Answer: 2. Solution: Co³⁺ d⁶ LS = −2.4Δo; Cr³⁺ d³ = −1.2Δo; ratio = 2. Trap: Treating Co(III)-oxalate as high spin — it's low spin. |
| 6. Diamagnetic Pair (2024 Jan 31) | Number of pairs containing ONLY diamagnetic species among the three Ni pairs. Answer: 1. Solution: [NiCl₄]²⁻ is para; only {[Ni(CO)₄], [Ni(CN)₄]²⁻} is fully diamagnetic. Trap: Misassigning Ni(0) oxidation state. |
| 7. EDTA Geometry (2024 Apr 9) | Coordination environment of Ca²⁺ with EDTA⁴⁻? Answer: Octahedral. Solution: EDTA⁴⁻ is hexadentate (2 N + 4 O) → CN 6 → octahedral. Trap: Overthinking the bulky chelate into a lower geometry. |
| 8. μ > 3.0 Sum (2026 Jan 21, NVQ) | Among Co²⁺, Ni²⁺, Fe²⁺, V³⁺, Ti²⁺ with μ > 3.0 BM — sum of unpaired electrons (high-spin octahedral)? Answer: 7. Solution: μ>3 → n≥3. Co²⁺ d⁷ (n=3) + Fe²⁺ d⁶ (n=4) = 7. Trap: Reading μ>3.0 as n>3; √15=3.87 so n=3 qualifies. |
| 9. en Valency (2025 Apr 7) | Primary and secondary valency of [Co(en)₂Cl₂]Cl? Answer: 3 and 6. Solution: OS = +3 (primary); CN = 2×2(en) + 2(Cl) = 6 (secondary). Trap: Counting en as monodentate → wrong CN of 4. |
| 10. Homoleptic Statement (2025 Apr 8) | S-I: homoleptic MA₆ shows no stereoisomerism. S-II: cis/trans-platin are Pd complexes. Answer: I true, II false. Solution: MA₆ is fully symmetric; platins are Pt, not Pd. Trap: Missing the Pd-for-Pt swap in statement II. |
| 11. Paramagnetic Count (2026 Jan 24) | Paramagnetic species among [CoF₆]³⁻, [TiF₆]³⁻, V₂O₅, [Fe(CN)₆]³⁻? Answer: 3. Solution: d⁶ HS para; d¹ para; V⁵⁺ d⁰ dia; d⁵ LS n=1 para → 3 paramagnetic. Trap: Miscounting V₂O₅ (V⁵⁺ = d⁰, diamagnetic). |
| 12. Formula from AgCl (2024 Apr 8, NVQ) | CoCl₃·nNH₃ gives 2 mol AgCl with excess AgNO₃. If OS of Co = x, find x+n. Answer: 8. Solution: 2 free Cl⁻ → [Co(NH₃)₅Cl]Cl₂, so n=5, x=3 → 8. Trap: Not locking Co(III) at CN 6. |
| 13. Unpaired Ordering (2026 Jan 24) | Increasing unpaired electrons: K₄[Fe(CN)₆], K₃[Fe(CN)₆], [Fe(H₂O)₆]SO₄·H₂O, [Fe(H₂O)₆]Cl₃. Answer: d⁶ LS (0) < d⁵ LS (1) < d⁶ HS (4) < d⁵ HS (5). Trap: Confusing spin states between Fe²⁺/Fe³⁺ with weak aquo ligands. |
| 14. Tetrahedral Splitting (2025 Apr 4) | True/False: in a tetrahedral field, the t₂ set (d_xy, d_yz, d_xz) is higher in energy than the e set. Answer: True. Solution: Tetrahedral splitting is inverted vs octahedral — t₂ above e. Trap: Carrying over octahedral t₂g/eg labels and assuming d_z² is highest. |
| 15. Freezing-Point Formula (2023 Apr 11, NVQ) | 0.1 m CrCl₃·xNH₃, ΔTf = 0.558°C, Kf = 1.86. Find the formula (CN 6, 100% ionisation). Answer: [Cr(NH₃)₅Cl]Cl₂. Solution: i = 0.558/(1.86×0.1) = 3 → 3 ions → [Cr(NH₃)₅Cl]Cl₂. Trap: Not linking van 't Hoff factor to the ionisation sphere. |
| 🎯 These are 15 of the 200+ JEE Main Coordination Compounds PYQs in the app. Drill all of them. | |
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| Every question above — including the compulsory NVQ type — is inside Logic Bloom, mapped across all shifts. Fill d-orbitals and compute CFSE, count isomers by rotating complexes, run stoichiometric sphere deductions. When a trap catches you, TarQ teaches the reasoning — not just the answer. Your Mistake Book tracks exactly which trap cost you — the pairing-energy omission, the d¹⁰ geometry slip, the trans-chirality error. Then take it into Battleground — 1v1 duels under real exam pressure. Get Logic Bloom — Free to start → |
How to Prepare Based on the Data
| 📌 Data-Driven Strategy for JEE Main Coordination Compounds | |
|---|---|
| Memorise the spectrochemical series with a mnemonic | It drives spin state, magnetic moment, hybridisation, and colour. Use the sentence device above — the extremes (halides weakest, CN⁻/CO strongest) are what NTA tests hardest. |
| Learn the CFSE table cold, and watch for P | This is the JEE-vs-NEET difference. Know the d¹–d¹⁰ values, and always check whether the question says "assume Δo ≫ P" before including or dropping the pairing term. |
| Master the Ni-trio and the d¹⁰ rule | [NiCl₄]²⁻ vs [Ni(CN)₄]²⁻ vs [Ni(CO)₄] is tested relentlessly. Strong-field doesn't always mean square planar — a d¹⁰ system can only be sp³ tetrahedral. |
| Drill isomer counting to fluency | cis is chiral, trans is achiral; MA₃B₃ gives fac/mer; square-planar MABCD gives 3. These are guaranteed NVQ integers with no partial credit. |
| Practise cross-chapter stoichiometry | AgCl mass and freezing-point depression to deduce the coordination sphere. This blends Mole Concept and colligative properties — a JEE signature. |
| Fill orbitals, count isomers, track your slips | Logic Bloom's Playground turns this chapter into interactive practice — compute CFSE, run the Ni-trio, count isomers — with TarQ teaching the reasoning. Drill every PYQ including NVQs, with your Mistake Book catching the pairing-energy and geometry errors. Then test under pressure in Battleground. Free to start. |
Building your JEE Main Inorganic base? This is the highest-ROI chapter in it.
| 🎯 2-3 questions per shift. Highest ROI in Inorganic. Rules, not rote. The patterns are here. The practice is in the app. | |
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| 🎮 Playground Understand through practice — with TarQ |
Every Coordination Compounds concept as interactive practice — fill t₂g/eg and watch CFSE and magnetic moment compute, rotate complexes to count optical isomers, run the Ni-trio side by side. Drill every PYQ across all shifts, including the NVQ type. When you're stuck, TarQ teaches the reasoning. Mistake Book catches the pairing-energy and geometry slips before the exam does. Get the app → |
| ⚔️ Battleground Score through practice — 1v1 duels |
NVQ enumeration rewards accuracy under pressure. Battleground trains exactly that — timed 1v1 duels across Physics, Chemistry, Biology, ELO climbing through 6 tiers. Get the app → |
| Understand through games. Score through practice. Get Logic Bloom — Free to start → |
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FAQs — Coordination Compounds JEE Main PYQ
Q1: How many questions come from Coordination Compounds in JEE Main?
It delivers 2-3 questions per shift, about 8-12% of the Chemistry paper. After the 2024 rationalisation deleted several rote-heavy Inorganic chapters, its weight rose further, making it the highest-ROI chapter in JEE Main Inorganic Chemistry.
Q2: How is JEE Main Coordination Compounds different from NEET?
JEE Main is far more calculation-driven. Where NEET asks whether a complex is paramagnetic, JEE makes you compute the exact CFSE, count total isomers, sum unpaired electrons across multiple complexes, and deduce the coordination sphere from AgCl precipitate mass or freezing-point depression — often as compulsory Numerical Value Questions with negative marking.
Q3: Why is [Ni(CO)₄] tetrahedral when CO is a strong-field ligand?
Because nickel in [Ni(CO)₄] is in the zero oxidation state, giving a d¹⁰ configuration. CO forces all electrons to pair, but a d¹⁰ system has no empty inner d-orbital available for dsp² hybridisation, so it can only form sp³ tetrahedral geometry. Strong-field does not automatically mean square planar — the d-electron count decides.
Q4: What is the most common CFSE trap in JEE Main?
Omitting the pairing energy. For a low-spin d⁶ complex the CFSE is −2.4Δo + 2P. Students write only −2.4Δo. When the question states "assume Δo ≫ P," the P term is ignored for ratio comparisons, but otherwise forgetting it gives a wrong answer. Always read whether the pairing energy should be included.
Q5: Are there actual JEE Main Coordination Compounds PYQs to practice?
Yes — this article contains 15 representative JEE Main PYQs with worked solutions and traps explained, including Numerical Value type. For the full set of 200+ JEE Main Coordination Compounds PYQs mapped across all shifts with TarQ teaching and a Mistake Book, download Logic Bloom. Free to start.
