Chapter 4: The d-and f-Block Elements Assertion-Reason Questions | chemistry Class 12 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): Zinc is not considered a transition element even though it belongs to the d-block. Reason (R): Zinc has a completely filled d¹⁰ configuration both in its ground state and in its common oxidation state (+2).

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): Transition metals generally exhibit high melting and boiling points. Reason (R): In transition metals, both (n-1)d electrons and ns electrons participate in interatomic metallic bonding, resulting in strong metallic bonds.

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 3

Logic Check

Assertion (A): Sc³⁺ and Ti⁴⁺ ions are colourless in aqueous solution. Reason (R): Both Sc³⁺ and Ti⁴⁺ have d⁰ configuration, so no d-d electronic transition is possible.

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 4

Logic Check

Assertion (A): Copper does not react with dilute sulphuric acid to liberate hydrogen. Reason (R): The standard electrode potential of copper, E°(Cu²⁺/Cu) = +0.34 V, is positive, placing it below hydrogen in the electrochemical series.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): The 5d transition series elements (like Hf) have nearly the same atomic radii as corresponding 4d elements (like Zr). Reason (R): This is a consequence of lanthanoid contraction, where filling of 4f orbitals causes a steady decrease in size that compensates for the expected increase in size from period 5 to period 6.

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 6

Logic Check

Assertion (A): Transition metals and their compounds show paramagnetic behaviour. Reason (R): Paramagnetism arises from the presence of paired electrons in d orbitals.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 7

Logic Check

Assertion (A): The enthalpies of atomisation of transition metals are higher than those of main group metals. Reason (R): Transition metals have a large number of unpaired electrons in their atoms, leading to stronger interatomic interactions and bonding.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): Cr has the electronic configuration [Ar] 3d⁵ 4s¹ instead of [Ar] 3d⁴ 4s². Reason (R): The half-filled 3d⁵ configuration has extra stability due to exchange energy, and the energy gap between 3d and 4s is very small.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 9

Logic Check

Assertion (A): Manganese (Z=25) exhibits all oxidation states from +2 to +7. Reason (R): Manganese has the configuration 3d⁵4s² and can use all seven outer electrons for bonding; its position near the middle of the series provides both the electrons and available orbitals for all these states.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): Cu⁺ is unstable in aqueous solution and disproportionates. Reason (R): The disproportionation 2Cu⁺ → Cu²⁺ + Cu is favoured because Cu²⁺ has a much higher hydration enthalpy than Cu⁺.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 11

Logic Check

Assertion (A): The variation in ionisation enthalpy along the first transition series is much less steep compared to the variation across a period of non-transition elements. Reason (R): In transition metals, the new electrons enter inner (n-1)d orbitals, which shield the outermost ns electrons more effectively from the increasing nuclear charge.

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 12

Logic Check

Assertion (A): The third ionisation enthalpy of Fe is lower than that of Mn. Reason (R): Removing an electron from Fe²⁺ (3d⁶) gives Fe³⁺ (3d⁵), a half-filled stable configuration, whereas removing an electron from Mn²⁺ (3d⁵) disrupts its stable half-filled configuration.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 13

Logic Check

Assertion (A): Interstitial compounds of transition metals are chemically inert and have high melting points. Reason (R): In interstitial compounds, small atoms (H, C, N) fill the interstitial spaces of the metal lattice, strengthening the structure and making it more resistant to chemical attack.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): Fluorine stabilises the highest oxidation state of transition metals in their halides. Reason (R): Fluorine has a small size and high electronegativity, providing either high lattice energy (for ionic fluorides) or high bond enthalpy (for covalent fluorides).

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 15

Logic Check

Assertion (A): Lanthanoids have only one stable oxidation state (+3) while actinoids exhibit a wide range of oxidation states. Reason (R): In lanthanoids, 4f orbitals are deeply buried; in actinoids, the 5f, 6d and 7s levels are of comparable energies allowing more electrons to participate in bonding.

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 16

Logic Check

Assertion (A): Transition metals form a large number of complex compounds. Reason (R): Transition metal ions are large in size, have low ionic charges and have no available d orbitals for bonding with ligands.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 17

Logic Check

Assertion (A): Potassium permanganate (KMnO4) acts as a stronger oxidising agent in acidic medium than in neutral or alkaline medium. Reason (R): In acidic medium, MnO4⁻ is reduced to Mn²⁺ (E° = +1.52 V), while in neutral medium it is reduced only to MnO2 (E° = +1.69 V).

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 18

Logic Check

Assertion (A): The density of transition metals generally increases across the first transition series from Sc to Cu. Reason (R): Atomic mass increases while metallic radius decreases across the series, so the mass per unit volume increases.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 19

Logic Check

Assertion (A): Ce⁴⁺ is a strong oxidising agent. Reason (R): Ce⁴⁺ has a noble-gas configuration (4f⁰) and readily accepts an electron to revert to the stable Ce³⁺ (4f¹) state.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 20

Logic Check

Assertion (A): The variability in oxidation states of transition elements arises from incomplete filling of d orbitals. Reason (R): The oxidation states of transition metals differ from each other by a unit of two, similar to non-transition elements.

Reasoning Options

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Chapter sections

Chapter 4: The d-and f-Block Elements | Assertion-Reason

Assertion (A): Zinc is not considered a transition element even though it belongs to the d-block. Reason (R): Zinc has a completely filled d¹⁰ configuration both in its ground state and in its common oxidation state (+2).

Assertion (A): Transition metals generally exhibit high melting and boiling points. Reason (R): In transition metals, both (n-1)d electrons and ns electrons participate in interatomic metallic bonding, resulting in strong metallic bonds.

Assertion (A): Sc³⁺ and Ti⁴⁺ ions are colourless in aqueous solution. Reason (R): Both Sc³⁺ and Ti⁴⁺ have d⁰ configuration, so no d-d electronic transition is possible.

Assertion (A): Copper does not react with dilute sulphuric acid to liberate hydrogen. Reason (R): The standard electrode potential of copper, E°(Cu²⁺/Cu) = +0.34 V, is positive, placing it below hydrogen in the electrochemical series.

Assertion (A): Transition metals and their compounds show paramagnetic behaviour. Reason (R): Paramagnetism arises from the presence of paired electrons in d orbitals.

Assertion (A): The enthalpies of atomisation of transition metals are higher than those of main group metals. Reason (R): Transition metals have a large number of unpaired electrons in their atoms, leading to stronger interatomic interactions and bonding.

Assertion (A): Cr has the electronic configuration [Ar] 3d⁵ 4s¹ instead of [Ar] 3d⁴ 4s². Reason (R): The half-filled 3d⁵ configuration has extra stability due to exchange energy, and the energy gap between 3d and 4s is very small.

Assertion (A): Manganese (Z=25) exhibits all oxidation states from +2 to +7. Reason (R): Manganese has the configuration 3d⁵4s² and can use all seven outer electrons for bonding; its position near the middle of the series provides both the electrons and available orbitals for all these states.

Assertion (A): Cu⁺ is unstable in aqueous solution and disproportionates. Reason (R): The disproportionation 2Cu⁺ → Cu²⁺ + Cu is favoured because Cu²⁺ has a much higher hydration enthalpy than Cu⁺.

Assertion (A): The third ionisation enthalpy of Fe is lower than that of Mn. Reason (R): Removing an electron from Fe²⁺ (3d⁶) gives Fe³⁺ (3d⁵), a half-filled stable configuration, whereas removing an electron from Mn²⁺ (3d⁵) disrupts its stable half-filled configuration.

Assertion (A): Interstitial compounds of transition metals are chemically inert and have high melting points. Reason (R): In interstitial compounds, small atoms (H, C, N) fill the interstitial spaces of the metal lattice, strengthening the structure and making it more resistant to chemical attack.

Assertion (A): Fluorine stabilises the highest oxidation state of transition metals in their halides. Reason (R): Fluorine has a small size and high electronegativity, providing either high lattice energy (for ionic fluorides) or high bond enthalpy (for covalent fluorides).

Assertion (A): Transition metals form a large number of complex compounds. Reason (R): Transition metal ions are large in size, have low ionic charges and have no available d orbitals for bonding with ligands.

Assertion (A): Potassium permanganate (KMnO4) acts as a stronger oxidising agent in acidic medium than in neutral or alkaline medium. Reason (R): In acidic medium, MnO4⁻ is reduced to Mn²⁺ (E° = +1.52 V), while in neutral medium it is reduced only to MnO2 (E° = +1.69 V).

Assertion (A): The density of transition metals generally increases across the first transition series from Sc to Cu. Reason (R): Atomic mass increases while metallic radius decreases across the series, so the mass per unit volume increases.

Assertion (A): Ce⁴⁺ is a strong oxidising agent. Reason (R): Ce⁴⁺ has a noble-gas configuration (4f⁰) and readily accepts an electron to revert to the stable Ce³⁺ (4f¹) state.

Assertion (A): The variability in oxidation states of transition elements arises from incomplete filling of d orbitals. Reason (R): The oxidation states of transition metals differ from each other by a unit of two, similar to non-transition elements.

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