The d and f Block Elements

The green paramagnetic species formed by heating KMnO₄ at 513 K is

NEET 2026

1K₂MnO₄

2Mn₃O₄

3MnO

4KO₂

NTA Answer: Option 1(final)

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Lesson: Catalytic Behaviour

NEET 2025

Match List-I with List-II. List-I List-II A. Haber process I. Fe catalyst B. Wacker oxidation II. PdCl2 C. Wilkinson catalyst III. [(PPh3)3RhCl] D Ziegler catalyst IV. TiCl4 with Al(CH3)3 Choose the correct answer from the options given below :

1A-I, B-IV, C-III, D-II

2A-I, B-II, C-IV, D-III

3A-II, B-III, C-I, D-IV

4A-I, B-II, C-III, D-IV

NTA Answer: Option 4(final)

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Given below are two statements : Statement I : Ferromagnetism is considered as an extreme form of paramagnetism. Statement II : The number of unpaired electrons in a Cr2+ ion (Z = 24) is the same as that of a Nd3+ ion (Z = 60). In the light of the above statements, choose the correct answer from the options given below :

NEET 2025

1Statement I is false but Statement II is true

2Both Statement I and Statement II are true

3Both Statement I and Statement II are false

4Statement I is true but Statement II is false

NTA Answer: Option 4(final)

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‘Spin only’ magnetic moment is same for which of the following ions? A. Ti3+ B. Cr2+ C. Mn2+ D. Fe2+ E. Sc3+ Choose the most appropriate answer from the options given below.

NEET 2024Revised key

1B and D only

2A and E only

3B and C only

4A and D only

NTA Answer: Option 1(revised_final)

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The E° value for the Mn3+/Mn2+ couple is more positive than that of Cr3+/Cr2+ or Fe3+/Fe2+ due to change of

NEET 2024Revised key

1d5 to d4 configuration

2d5 to d2 configuration

3d4 to d5 configuration

4d3 to d5 configuration

NTA Answer: Option 3(revised_final)

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Lesson: Lanthanoids

NEET 2024Revised key

The pair of lanthanoid ions which are diamagnetic is

1Ce4+ and Yb2+

2Ce3+ and Eu2+

3Gd3+ and Eu3+

4Pm3+ and Sm3+

NTA Answer: Option 1(revised_final)

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The stability of Cu2+ is more than Cu+ salts in aqueous solution due to

NEET 2023

1Enthalpy of atomization

2Hydration energy

3Second ionisation enthalpy

4First ionisation enthalpy

NTA Answer: Option 2(final)

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Which of the following statements are INCORRECT? A. All the transition metals except scandium form MO oxides which are ionic. B. The highest oxidation number corresponding to the group number in transition metal oxides is attained in Sc₂O₃ to Mn₂O₇. C. Basic character increases from V₂O₃ to V₂O₄ to V₂O₅. D. V₂O₄ dissolves in acids to give VO₄³⁻ salts. E. CrO is basic but Cr₂O₃ is amphoteric. Choose the correct answer from the options given below:

NEET 2023

1B and D only

2C and D only

3B and C only

4A and E only

NTA Answer: Option 2(final)

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Lesson: Lanthanoids

NEET 2022

Gadolinium has a low value of third ionisation enthalpy because of

1high basic character

2small size

3high exchange enthalpy

4high electronegativity

NTA Answer: Option 3(final)

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In the neutral or faintly alkaline medium, KMnO 4 oxidises iodide into iodate. The change in oxidation state of manganese in this reaction is from

NEET 2022

1+6 to +5

2+7 to +4

3+6 to +4

4+7 to +3

NTA Answer: Option 2(final)

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Lesson: Lanthanoids

NEET 2021

The incorrect statement among the following is :

1Actinoids are highly reactive metals, especially when finely divided.

2Actinoid contraction is greater for element to element than lanthanoid contraction

3Most of the trivalent Lanthanoid ions are colorless in the solid state

4Lanthanoids are good conductors of heat and electricity

NTA Answer: Option 3(final)

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The calculated spin only magnetic moment of Cr2+ ion is :

NEET 2020

12.84 BM

23.87 BM

34.90 BM

45.92 BM

NTA Answer: Option 3(final)

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Identify the incorrect statement.

NEET 2020

1The oxidation states of chromium in CrO₄²⁻ and Cr₂O₇²⁻ are not the same.

2Cr2+(d4 ) is a stronger reducing agent than Fe2+(d6 ) in water.

3The transition metals and their compounds are known for their catalytic activity due to their ability to adopt multiple oxidation states and to form complexes.

4Interstitial compounds are those that are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals.

NTA Answer: Option 1(final)

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Exam traps and common mistakes in this unit

Trap

KMnO4 oxidation product depends on medium

Category: Inorganic Exception

Student assumes Mn²⁺ is the product regardless of medium. Acidic: → Mn²⁺ (5e⁻). Neutral/weakly basic: → MnO₂ (3e⁻). Strongly basic: → MnO₄²⁻ (1e⁻).

When it triggers

Question gives KMnO4 oxidation in unspecified or specific medium.

How to avoid

Always check medium. In acidic: Mn(+7) → Mn(+2). In neutral: → Mn(+4) (MnO₂). In basic: → Mn(+6) (manganate). The number of electrons (n) in Nernst calculations depends accordingly.

Mistake

Assumes Mn²⁺ is the product of KMnO₄ reduction in any medium.

Root cause: concept gap

Correction

Acidic: → Mn²⁺ (5e⁻). Neutral/weakly basic: → MnO₂ (3e⁻). Strongly basic: → MnO₄²⁻ (1e⁻).

Lesson: Lanthanoids

Mistake

Predicts that 5d-block elements have much larger size than 4d.

Root cause: concept gap

Correction

Lanthanoid contraction (imperfect 4f shielding) makes 5d elements similar in size to 4d. Zr/Hf, Nb/Ta, Mo/W have nearly identical chemistry.

Formulas in this unit

Spin-only magnetic moment

μ = n (n + 2) BM

Magnetic moment from n unpaired electrons. 1 unpaired: 1.73 BM; 5: 5.92 BM.

Symbol	Quantity	SI Unit
n	unpaired electrons	-
mu	magnetic moment	Bohr magneton

Valid when

Spin-only contribution (no orbital contribution)
Octahedral or tetrahedral complex

Spin-only magnetic moment for transition metal

μ = n (n + 2) BM

Predicts paramagnetic moment of d-block ion. n unpaired electrons in d-orbitals.

Symbol	Quantity	SI Unit
n	unpaired electrons	-
mu	magnetic moment	BM

Valid when

Spin-only contribution
Octahedral or tetrahedral complex
First-row d-block

Common oxidation states (first-row TM)

Mn: + 2 \to + 7; Cr: + 2 \to + 6

Catalogues common stable oxidation states across first-row transition metals.

Symbol	Quantity	SI Unit
OS	oxidation state	-

Valid when

First-row d-block
Common (not exotic) compounds

NEET question patterns in this unit

Use KMnO4 or K2Cr2O7 in acidic/neutral/basic medium for oxidation. Different products by medium.

InterpretationMedium

Common distractors

uses acidic formula in basic medium

Assumes Mn²⁺ regardless of medium

Lesson: Lanthanoids

Effect of lanthanoid contraction on properties of 4d/5d transition metals. Closer atomic/ionic radii, similar properties (Zr/Hf, Nb/Ta).

RecallEasy

Common distractors

predicts large difference due to period shift

Expects 5d to be much larger than 4d