Which formulas matter most in d and f Block Elements and Coordination Compounds?

The d and f Block Elements and Coordination Compounds sheet on this page has 10 formula entries, starting with General Electronic Configuration of d-Block Elements, Magnetic Moment Formula, Color of Transition Metal Complexes, Crystal Field Splitting Energy (CFSE) for Octahedral Complexes, Effective Atomic Number (EAN). Each one comes with when to use it and the trap to avoid.

What topics does d and f Block Elements and Coordination Compounds cover for JEE?

d and f Block Elements and Coordination Compounds covers Transition Elements, Lanthanides and Actinides, Coordination Compounds, Nomenclature of Complexes, Crystal Field Theory, Isomerism in Complexes.

d and f Block Elements and Coordination Compounds for JEE Main & Advanced — formulas, what is asked, and traps

JEEGenie estimates about 6% of JEE Main marks come from d and f Block Elements and Coordination Compounds. This page covers 10 formula entries, each with when to use it, what JEE asks and the traps. A common slip: Forgetting that Cr is 3d⁵4s¹, not 3d⁴4s².

Key points to know

General Electronic Configuration of d-Block Elements. d-block elements have valence electrons in (n-1)d orbitals, with general configuration (n-1)d¹⁻¹⁰ ns¹⁻². Exceptions: Cr and Cu due to half-filled and fully-filled stability.
Lanthanoid Contraction. Steady decrease in atomic and ionic radii of lanthanoids (La to Lu) due to poor shielding of 4f electrons, increasing effective nuclear charge.
Oxidation States of d-Block Elements. Transition metals show variable oxidation states due to small energy gap between (n-1)d and ns orbitals. Highest oxidation state increases across period up to Mn (+7), then decreases.
Coordination Entity and Central Atom. A coordination compound consists of a central metal atom/ion bonded to ligands via coordinate bonds. The coordination number is the number of ligand donor atoms attached.
Werner's Theory. Metals have primary (ionizable) and secondary (non-ionizable) valencies. Primary valency equals oxidation state, secondary valency equals coordination number.
Ligand and Its Types. Ligands are ions or molecules that donate electron pairs to metal. Types: monodentate (one donor atom), bidentate (two), polydentate (many). Ambidentate ligands can bind through different atoms.
Spectrochemical Series. Order of ligands by their ability to split d-orbitals: I⁻ < Br⁻ < S²⁻ < SCN⁻ < Cl⁻ < NO₃⁻ < F⁻ < OH⁻ < H₂O < NH₃ < en < NO₂⁻ < CN⁻ < CO. Strong field ligands cause large Δ and low-spin complexes.
f-Block Elements: Lanthanoids and Actinoids. Lanthanoids (4f series, La to Lu) and actinoids (5f series, Ac to Lr) have f-orbitals filling. Actinoids are radioactive and show more variable oxidation states due to smaller energy gap.
Magnetic Properties of Coordination Compounds. Paramagnetic if unpaired electrons present; diamagnetic if all paired. Spin-only formula μ = √[n(n+2)] BM. Low-spin complexes are less paramagnetic than high-spin for same metal ion.
Important Reactions of d-Block Elements. Key reactions: K₂Cr₂O₇ + H₂SO₄ → chromic acid (oxidation); KMnO₄ in acidic medium acts as strong oxidizer (Mn²⁺); Fe³⁺ + SCN⁻ → blood-red complex.
Coordination Number and Geometry. Common coordination numbers: 2 (linear), 4 (tetrahedral or square planar), 6 (octahedral). Geometry depends on metal, ligand, and oxidation state.
Applications of Coordination Compounds. Used in: metallurgy (extraction of Ag, Au via cyanide complex), water softening (EDTA), biological systems (hemoglobin, chlorophyll), and as catalysts.

Formula sheet

Name	Formula	When to use
General Electronic Configuration of d-Block Elements	$(n - 1) d^{1 - 10} n s^{1 - 2}$	When determining electronic configuration of transition metals or predicting their properties.
Magnetic Moment Formula	$μ = \sqrt{n (n + 2)} BM$	Calculating magnetic moment from number of unpaired electrons or vice versa, especially for transition metal complexes.
Color of Transition Metal Complexes	$Δ_{oct} = energy of d-d transition$	Explaining or predicting color of transition metal ions/complexes based on oxidation state and ligand.
Crystal Field Splitting Energy (CFSE) for Octahedral Complexes	$CFSE = (- 0.4 Δ_{o} \times n_{t_{2 g}}) + (0.6 Δ_{o} \times n_{e_{g}})$	Calculating stabilization energy to predict geometry, spin state, or magnetic properties.
Effective Atomic Number (EAN)	$EAN = Z_{metal} - oxidation state + 2 \times coordination number$	Predicting stability of metal carbonyls or organometallic complexes.
Stability Constant (K_f) and Instability Constant (K_d)	$K_{f} = \frac{[M L_{n}]}{[M] [L]^{n}}$	Comparing stability of complexes or predicting displacement reactions.
Magnetic Properties of Coordination Compounds	$μ = \sqrt{n (n + 2)} BM$	Predicting magnetic behavior from electronic configuration and ligand field strength.
Crystal Field Splitting in Tetrahedral Complexes	$Δ_{t} = \frac{4}{9} Δ_{o}$	Predicting geometry and spin state for tetrahedral complexes like [CoCl₄]²⁻.
Important Reactions of d-Block Elements	${Cr}_{2} O_{7}^{2 -} + 14 H^{+} + 6 e^{-} \to 2 {Cr}^{3 +} + 7 H_{2} O$	Solving redox reactions and qualitative analysis problems.
Applications of Coordination Compounds	$4 Au + 8 {CN}^{-} + O_{2} + 2 H_{2} O \to 4 [{Au(CN)}_{2}]^{-} + 4 {OH}^{-}$	Connecting coordination chemistry to real-world applications.

Open the d and f Block Elements and Coordination Compounds formula page

What JEE asks

General Electronic Configuration of d-Block Elements. JEE often asks for the configuration of specific elements like Cr, Cu, or Mo, testing the stability of half-filled and fully-filled d-subshells.
Lanthanoid Contraction. JEE frequently tests the consequence: similar properties of 4d and 5d transition metals due to lanthanoid contraction.
Magnetic Moment Formula. JEE often asks to find the number of unpaired electrons from given μ value, or predict μ for a given ion.
Color of Transition Metal Complexes. JEE tests why certain ions (e.g., Cu²⁺ blue, Ni²⁺ green) are colored, and why Zn²⁺ is colorless.
Oxidation States of d-Block Elements. JEE often asks for the most stable oxidation state of an element (e.g., Fe³⁺ > Fe²⁺ due to half-filled d⁵).
Coordination Entity and Central Atom. JEE tests the definition and asks to find coordination number from formula or vice versa.
Crystal Field Splitting Energy (CFSE) for Octahedral Complexes. JEE often asks to compare CFSE of high-spin vs low-spin for d⁴, d⁵, d⁶, d⁷ ions.
Naming Coordination Compounds (IUPAC). JEE often gives a complex formula and asks for its correct IUPAC name, testing order and oxidation state.
Werner's Theory. JEE tests the concept of primary and secondary valency in simple complexes like CoCl₃·6NH₃.
Effective Atomic Number (EAN). JEE often asks to calculate EAN for complexes like [Fe(CO)₅] or [Ni(CO)₄].
Ligand and Its Types. JEE tests examples: en (bidentate), EDTA (hexadentate), SCN⁻ (ambidentate).
Isomerism in Coordination Compounds. JEE often asks for number of geometrical isomers for [Ma₂b₂] or [M(AA)₂] type complexes.
Spectrochemical Series. JEE tests the order and asks which ligand causes maximum splitting or which complex is low-spin.
Stability Constant (K_f) and Instability Constant (K_d). JEE may ask to calculate concentration of free metal ion from K_f and ligand concentration.
Chelate Effect. JEE tests the thermodynamic reason (entropy) and examples of chelating ligands.
f-Block Elements: Lanthanoids and Actinoids. JEE often asks for the number of elements in each series (14 each) and the most common oxidation state (+3).
Magnetic Properties of Coordination Compounds. JEE tests comparison of magnetic moments for high-spin vs low-spin (e.g., [Fe(H₂O)₆]²⁺ vs [Fe(CN)₆]⁴⁻).
Crystal Field Splitting in Tetrahedral Complexes. JEE may ask to compare CFSE of tetrahedral vs octahedral for same metal ion.
Valence Bond Theory (VBT) for Coordination Compounds. JEE tests hybridization of metal in complexes like [Ni(CN)₄]²⁻ (dsp²) vs [NiCl₄]²⁻ (sp³).
Important Reactions of d-Block Elements. JEE often asks for products of oxidation reactions using K₂Cr₂O₇ or KMnO₄.
Coordination Number and Geometry. JEE tests geometry of complexes like [Pt(NH₃)₂Cl₂] (square planar) vs [Zn(NH₃)₄]²⁺ (tetrahedral).
Linkage Isomerism. JEE often asks for examples: [Co(NH₃)₅NO₂]²⁺ has two isomers (nitro and nitrito).
Applications of Coordination Compounds. JEE tests the role of [Ag(CN)₂]⁻ in silver extraction or EDTA in hard water treatment.

Common traps

Forgetting that Cr is 3d⁵4s¹, not 3d⁴4s². General Electronic Configuration of d-Block Elements
Confusing lanthanoid contraction with actinoid contraction; both occur but for different f-orbitals. Lanthanoid Contraction
Using n as total electrons instead of unpaired electrons. Magnetic Moment Formula
Assuming all transition metal compounds are colored; Sc³⁺ and Ti⁴⁺ are colorless due to d⁰ configuration. Color of Transition Metal Complexes
Thinking all d-block elements show +2 state; Zn shows only +2, Sc shows +3. Oxidation States of d-Block Elements
Confusing coordination number with number of ligands; e.g., [Co(en)₃]³⁺ has CN=6 but 3 ligands. Coordination Entity and Central Atom
Forgetting to account for pairing energy in low-spin complexes. Crystal Field Splitting Energy (CFSE) for Octahedral Complexes
Not alphabetizing ligands correctly; e.g., 'ammine' before 'chloro'. Naming Coordination Compounds (IUPAC)
Thinking primary valency can be satisfied by neutral molecules; it is satisfied only by anions (secondary valency by neutral molecules or anions). Werner's Theory
Forgetting to subtract oxidation state first. Effective Atomic Number (EAN)
Thinking EDTA is bidentate or tetradentate; it is hexadentate, with 6 donor atoms (4 O and 2 N). Ligand and Its Types
Assuming all octahedral complexes show geometrical isomerism; [Co(NH₃)₆]³⁺ has none. Isomerism in Coordination Compounds
Placing H₂O before NH₃; NH₃ is stronger than H₂O. Spectrochemical Series
Confusing K_f with K_d; they are reciprocals. Stability Constant (K_f) and Instability Constant (K_d)

Topics in d and f Block Elements and Coordination Compounds

Transition Elements
Lanthanides and Actinides
Coordination Compounds
Nomenclature of Complexes
Crystal Field Theory
Isomerism in Complexes

Previous-year questions on d and f Block Elements and Coordination Compounds

JEEGenie has 932 previous-year questions on d and f Block Elements and Coordination Compounds. A few worked examples follow.

Year	Questions
2026	57
2025	66
2024	89
2023	79
2022	63
2021	83
2020	46
2019	80
2018	26
2017	13
2016	25
2015	22
2014	13
2013	17
2012	13
2011	11
2010	9
2009	8
2008	11
2007	6
2006	12
2005	14
2004	18
2003	15
2002	11
2001	4
2000	10
1999	7
1998	10
1997	6
1996	6
1995	3
1994	9
1993	7
1992	2
1991	5
1990	7
1989	2
1988	8
1987	8
1986	5
1985	3
1984	3
1983	4
1982	4
1981	3
1980	6
1979	3

Question 1 easy

Which of the following sets includes all the species that will change the orange colour of

K_{2} C r_{2} O_{7}

in acidic medium?

$F e^{2 +}, S n^{2 +}, I^{-}, S^{2 -}$
$S^{2 -}, F e^{3 +}, I^{-}, C_{2} O_{4}^{2 -}$
$F e^{2 +}, N O_{2}^{-}, S O_{2}, S n^{4 +}$
$F e^{3 +}, S O_{4}^{2 -}, S^{2 -}, S n^{4 +}$

Answer: A

Explanation. In acidic medium,

K_{2} C r_{2} O_{7}

acts as a strong oxidising agent, changing from orange

C r_{2} O_{7}^{2 -}

to green

C r^{3 +}

. It will change colour only if the added species is a reducing agent. 1. **Identify the oxidising power**:

C r_{2} O_{7}^{2 -} + 14 H^{+} + 6 e^{-} \to 2 C r^{3 +} + 7 H_{2} O

So, any species that can be oxidised (i.e., a reductant) will cause the colour change. 2. **Check each option for reducing agents**: - **Option A**:

F e^{2 +} \to F e^{3 +} + e^{-}

(reducing agent)

S n^{2 +} \to S n^{4 +} + 2 e^{-}

(reducing agent)

2 I^{-} \to I_{2} + 2 e^{-}

(reducing agent)

S^{2 -} \to S + 2 e^{-}

(reducing agent) All four are reducing agents

\to

colour change occurs. - **Option B**:

F e^{3 +}

is already oxidised, not a reducing agent

\to

no colour change. - **Option C**:

S n^{4 +}

is already oxidised, not a reducing agent

\to

no colour change. - **Option D**:

F e^{3 +}, S O_{4}^{2 -}, S n^{4 +}

are all oxidised forms

\to

no colour change. 3. **Conclusion**: Only option A contains all reducing species that will reduce

C r_{2} O_{7}^{2 -}

and change its colour.

A

From NTA/IIT papers: JEE Main 2026 · 2 Apr Shift 1

Question 2 medium

A transition metal (M) among

M n, C r, C o

and Fe has the highest standard electrode potential

(M^{3 +} / M^{2 +})

. It forms a metal complex of the type

{[M (C N)_{6}]}^{4 -}

. The number of electrons present in the

e_{g}

orbital of the complex is ___________.

Answer: 1

Explanation. For

{M n}^{3 +} / {M n}^{2 +}

E^{\circ} = + 1.51 V

For

{C r}^{3 +} / {C r}^{2 +}

E^{\circ} = - 0.41 V

For

{C o}^{3 +} / {C o}^{2 +}

E^{\circ} = + 1.82 V

For

{F e}^{3 +} / {F e}^{2 +}

E^{\circ} = + 0.77 V

Thus, the metal with the highest

E^{\circ}

C o

. In

{[C o (C N)_{6}]}^{4 -}

, Co is in +2 oxidation state:

{C o}^{2 +}

3 d^{7}

configuration.

C N^{-}

is a strong-field ligand, so the complex is low-spin. For

d^{7}

in octahedral low-spin:

t_{2 g}^{6} e_{g}^{1}

. Therefore, the number of electrons in the

e_{g}

orbital is:

1

From NTA/IIT papers: JEE Main 2025 · 2 Apr Shift 1

Question 3 hard

The number of complexes from the following with no electrons in the

t_{2}

orbital is ______.

{T i C l}_{4}, {[{M n O}_{4}]}^{-}, {[{F e O}_{4}]}^{2 -}, {[{F e C l}_{4}]}^{-}, {[{C o C l}_{4}]}^{2 -}

Answer: C

Explanation. To determine how many complexes have no electrons in the

t_{2}

orbital, we need to analyze the electronic configuration and geometry of each complex. **1.

T i C l_{4}

** - Ti oxidation state:

+ 4

\to T i^{4 +}

3 d^{0}

- Cl^{-} is a weak field ligand, but with

d^{0}

, no electrons in d-orbitals at all. - Geometry: tetrahedral. - In tetrahedral splitting, orbitals split into

e

(lower) and

t_{2}

(higher). -

d^{0}

means **zero electrons in

t_{2}

**. ✅ **2.

[M n O_{4}]^{-}

** - Mn oxidation state:

+ 7

\to M n^{7 +}

3 d^{0}

- Tetrahedral geometry (permanganate ion). -

d^{0} \to

no electrons in

t_{2}

. ✅ **3.

[F e O_{4}]^{2 -}

** - Fe oxidation state:

+ 6

\to F e^{6 +}

3 d^{2}

- Tetrahedral geometry (ferrate ion). - In tetrahedral field:

e

lower,

t_{2}

higher. -

d^{2}

electrons go into

e

orbitals (lower energy) according to Hund’s rule. -

t_{2}

remains empty. ✅ **4.

[F e C l_{4}]^{-}

** - Fe oxidation state:

+ 3

\to F e^{3 +}

3 d^{5}

- Cl^{-} weak field, tetrahedral complex. - Tetrahedral splitting:

e

(2 orbitals) lower,

t_{2}

(3 orbitals) higher. - For

d^{5}

in tetrahedral weak field: electrons fill all 5 d-orbitals singly (high spin). - That means

e^{2} t_{2}^{3} \to t_{2}

has 3 electrons. ❌ **5.

[C o C l_{4}]^{2 -}

** - Co oxidation state:

+ 2

\to C o^{2 +}

3 d^{7}

- Cl^{-} weak field, tetrahedral. - Tetrahedral splitting:

e

lower,

t_{2}

higher. -

d^{7}

in tetrahedral:

e^{4} t_{2}^{3}

(high spin). -

t_{2}

has 3 electrons. ❌ **Summary:** -

T i C l_{4}

t_{2}^{0}

✅ -

[M n O_{4}]^{-}

t_{2}^{0}

✅ -

[F e O_{4}]^{2 -}

t_{2}^{0}

✅ -

[F e C l_{4}]^{-}

t_{2}^{3}

❌ -

[C o C l_{4}]^{2 -}

t_{2}^{3}

❌ Number with no electrons in

t_{2}

orbital = **3**. Answer: (C)

From NTA/IIT papers: JEE Main 2024 · 5 Apr Shift 2

Question 4 medium

Strong reducing and oxidizing agents among the following, respectively, are :

${C e}^{4 +} a n d {E u}^{2 +}$
${E u}^{2 +} a n d {C e}^{4 +}$
${C e}^{4 +} a n d {T b}^{4 +}$
${C e}^{3 +} a n d {C e}^{4 +}$

Answer: B

Explanation. For lanthanoids, the most stable oxidation state is

+ 3

. A species is a strong reducing agent if it easily gets oxidized to a more stable state.

{E u}^{2 +}

has the electronic configuration

[X e] 4 f^{7}

, which is half-filled and stable. It readily loses one electron to form

{E u}^{3 +}

(

[X e] 4 f^{6}

), so

{E u}^{2 +}

is a strong reducing agent. A species is a strong oxidizing agent if it easily gets reduced to a more stable state.

{C e}^{4 +}

has configuration

[X e]

, which is the noble gas configuration, and it readily gains one electron to form

{C e}^{3 +}

(

[X e] 4 f^{1}

). Thus,

{C e}^{4 +}

is a strong oxidizing agent. Therefore, the strong reducing agent is

{E u}^{2 +}

and the strong oxidizing agent is

{C e}^{4 +}

B) {E u}^{2 +} and {C e}^{4 +}

From NTA/IIT papers: JEE Main 2023 · 6 Apr Shift 1

Question 5 hard

Atom X occupies the fcc lattice sites as well as alternate tetrahedral voids of the same lattice. The packing efficiency (in %) of the resultant solid is closest to

Answer: B

Explanation. **Atoms per cell.** An fcc cell holds

4

lattice atoms and has

8

tetrahedral voids. Filling alternate voids adds

4

more atoms of X, so there are

8

atoms of X per cell. **Radius.** All the atoms are X, so they all have the same radius

r

. A tetrahedral void sits at

(\frac{a}{4}, \frac{a}{4}, \frac{a}{4})

, a quarter of the way along the body diagonal from a corner. Its distance from the corner atom is therefore

d = \frac{\sqrt{3} a}{4} .

Two X atoms in contact are

2 r

apart, so

2 r = \frac{\sqrt{3} a}{4} \Rightarrow r = \frac{\sqrt{3} a}{8} .

At this radius the fcc lattice atoms do not touch each other, because

4 r = \frac{\sqrt{3}}{2} a < \sqrt{2} a

. The void–corner contact is therefore the one that fixes the cell size. **Packing efficiency.**

PE = \frac{8 \times \frac{4}{3} π r^{3}}{a^{3}} = \frac{32 π}{3} {(\frac{\sqrt{3}}{8})}^{3} = \frac{32 π}{3} \cdot \frac{3 \sqrt{3}}{512} = \frac{\sqrt{3} π}{16} \approx 0.340.

That is about

34 %

, and the closest option is

35 %

. Answer: (B)

From NTA/IIT papers: JEE Advanced 2022

Frequently asked questions

How much of JEE Main comes from d and f Block Elements and Coordination Compounds?: JEEGenie estimates about 6% of JEE Main marks come from d and f Block Elements and Coordination Compounds, based on recent papers. The share varies from year to year.
Which formulas matter most in d and f Block Elements and Coordination Compounds?: The d and f Block Elements and Coordination Compounds sheet on this page has 10 formula entries, starting with General Electronic Configuration of d-Block Elements, Magnetic Moment Formula, Color of Transition Metal Complexes, Crystal Field Splitting Energy (CFSE) for Octahedral Complexes, Effective Atomic Number (EAN). Each one comes with when to use it and the trap to avoid.
What topics does d and f Block Elements and Coordination Compounds cover for JEE?: d and f Block Elements and Coordination Compounds covers Transition Elements, Lanthanides and Actinides, Coordination Compounds, Nomenclature of Complexes, Crystal Field Theory, Isomerism in Complexes.
How should I revise d and f Block Elements and Coordination Compounds before the exam?: Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens d and f Block Elements and Coordination Compounds questions on JEEGenie.
How many previous-year questions are there on d and f Block Elements and Coordination Compounds?: JEEGenie has 932 previous-year questions on d and f Block Elements and Coordination Compounds, and this page shows a few with worked explanations.
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