ROUTERA

Chapter 8 The d and f Block Elements

Class 12th Chemistry Chapter Assertion and Reason

Here are the 50 Assertion and Reason questions for Chapter 8: The d and f Block Elements of Class 12 Chemistry based on the NCERT syllabus.

Options

(1) Assertion is true, Reason is true, and Reason is the correct explanation of Assertion.
(2) Assertion is true, Reason is true, but Reason is not the correct explanation of Assertion.
(3) Assertion is true, but Reason is false.
(4) Assertion is false, but Reason is true.
(5) Both Assertion and Reason are false.

1. Assertion (A): Transition elements exhibit a wide range of oxidation states.

Reason (R): The transition elements have relatively small ionization enthalpies and comparable energies of the 4s and 3d orbitals, which facilitates the loss of varying numbers of electrons.

Answer: (1)
Explanation: Transition elements show a wide range of oxidation states because their 3d and 4s orbitals are close in energy, allowing them to lose varying numbers of electrons.

2. Assertion (A): The electronic configuration of Cr is [Ar] 3d⁵ 4s¹.

Reason (R): Chromium has an exceptionally stable half-filled d-subshell configuration.

Answer: (1)
Explanation: Chromium has a half-filled d-subshell configuration (3d⁵) which provides extra stability, leading to the electronic configuration [Ar] 3d⁵ 4s¹.

3. Assertion (A): Lanthanides show a +3 oxidation state predominantly.

Reason (R): Lanthanides have a stable electronic configuration with 3 electrons in the 4f subshell.

Answer: (4)
Explanation: The +3 oxidation state in lanthanides is predominant because the loss of three electrons from the 4f and 6s orbitals results in a stable configuration. However, it is not due to the 4f subshell having exactly 3 electrons.

4. Assertion (A): The transition metals are good conductors of heat and electricity.

Reason (R): The presence of unpaired electrons in the d-orbitals contributes to electrical conductivity.

Answer: (1)
Explanation: Transition metals have free electrons in the d-orbitals, which allows them to conduct heat and electricity efficiently.

5. Assertion (A): The d-block elements exhibit magnetic properties.

Reason (R): The presence of unpaired electrons in the d-orbitals leads to paramagnetism.

Answer: (1)
Explanation: The unpaired electrons in the d-orbitals of transition metals lead to paramagnetism, causing the d-block elements to exhibit magnetic properties.

6. Assertion (A): Actinides are more reactive than lanthanides.

Reason (R): Actinides have a larger atomic size and lower ionization enthalpy compared to lanthanides.

Answer: (1)
Explanation: The larger size and lower ionization enthalpy of actinides make them more reactive compared to lanthanides.

7. Assertion (A): The transition elements form colored compounds.

Reason (R): The d-d transitions in the electronic structure of transition metal ions give rise to visible absorption and color.

Answer: (1)
Explanation: The absorption of light in the visible region, due to d-d transitions in the electronic structure of transition metal ions, leads to the formation of colored compounds.

8. Assertion (A): Copper (Cu) exhibits a +1 oxidation state in some of its compounds.

Reason (R): The 4s electron in Cu can be removed easily, resulting in a +1 oxidation state.

Answer: (1)
Explanation: The +1 oxidation state of copper is stable because the removal of one electron from the 4s orbital results in a stable electronic configuration.

9. Assertion (A): The first ionization enthalpy of transition elements is higher than that of s-block elements.

Reason (R): Transition elements have a larger nuclear charge and smaller atomic radius, which makes it harder to remove electrons.

Answer: (1)
Explanation: The higher nuclear charge and smaller atomic radius in transition elements make it harder to remove electrons, leading to a higher first ionization enthalpy compared to s-block elements.

10. Assertion (A): The lanthanide contraction leads to similar ionic radii of lanthanides and transition metals.

Reason (R): The gradual decrease in size across the lanthanide series causes the ionic radii of lanthanides and transition metals to overlap.

Answer: (1)
Explanation: The lanthanide contraction, due to poor shielding by the 4f electrons, causes a decrease in the size of lanthanide ions, leading to similar ionic radii with transition metals.

11. Assertion (A): Manganese (Mn) shows the maximum oxidation state of +7 in MnO₄⁻.

Reason (R): Manganese has a high ionization enthalpy and can lose 7 electrons to form MnO₄⁻.

Answer: (1)
Explanation: Manganese can achieve a +7 oxidation state in MnO₄⁻ due to the availability of 7 valence electrons that can be ionized, allowing it to form this highly oxidized state.

12. Assertion (A): Zinc is not considered a transition element.

Reason (R): Zinc has a completely filled d-orbital (3d¹⁰), making it chemically inert.

Answer: (1)
Explanation: Zinc does not exhibit typical transition element properties because it has a fully filled 3d¹⁰ configuration and does not form variable oxidation states.

13. Assertion (A): The d-block elements are hard and have high melting points.

Reason (R): The strong metallic bonding in d-block elements, due to the presence of delocalized d-electrons, accounts for their hardness and high melting points.

Answer: (1)
Explanation: The strong metallic bonding in transition metals, where d-electrons are delocalized, contributes to their hardness and high melting points.

14. Assertion (A): The oxidation state of iron in Fe₂O₃ is +3.

Reason (R): Iron loses three electrons to form the Fe³⁺ ion in Fe₂O₃.

Answer: (1)
Explanation: In Fe₂O₃, iron exhibits a +3 oxidation state as it loses three electrons to form Fe³⁺ ions.

15. Assertion (A): The d-orbital in transition metals is involved in bonding.

Reason (R): The availability of d-electrons in the transition metals allows them to form multiple bonds with ligands.

Answer: (1)
Explanation: The d-orbitals in transition metals are involved in bonding, enabling them to form coordination compounds with various ligands.

16. Assertion (A): The transition metals have high density.

Reason (R): The transition elements have a high atomic mass and small atomic size, which leads to a higher density.

Answer: (1)
Explanation: The small atomic size and high atomic mass of transition metals result in a high density.

17. Assertion (A): Lanthanides and actinides are known as inner transition elements.

Reason (R): These elements fill the 4f and 5f orbitals, respectively, which are inner orbitals in the periodic table.

Answer: (1)
Explanation: Lanthanides and actinides are called inner transition elements because they fill the 4f and 5f orbitals, which are inner orbitals.

18. Assertion (A): The color of a compound depends on the nature of the ligands and the metal center.

Reason (R): The metal-ligand interactions cause d-d transitions that are responsible for the color of the compound.

Answer: (1)
Explanation: The color of coordination compounds is due to d-d transitions caused by the interaction between the metal and the ligands.

19. Assertion (A): The transition metals form complex ions with ligands.

Reason (R): The ability of transition metals to use their empty d-orbitals allows them to form coordination complexes with ligands.

Answer: (1)
Explanation: Transition metals have empty d-orbitals that can accommodate ligands, leading to the formation of complex ions.

20. Assertion (A): The f-block elements are more reactive than the d-block elements.

Reason (R): The f-block elements have a larger size and lower ionization enthalpy, making them more reactive than the d-block elements.

Answer: (1)
Explanation: The larger size and lower ionization enthalpy of f-block elements contribute to their higher reactivity compared to d-block elements.

21. Assertion (A): Chromium forms a variety of complex compounds.

Reason (R): Chromium has an unpaired electron in its d-orbitals, which allows it to form stable coordination complexes.

Answer: (1)
Explanation: The presence of unpaired electrons in the d-orbitals of chromium allows it to form a wide variety of stable coordination compounds.

22. Assertion (A): The first ionization enthalpy of transition elements is higher than that of alkali metals.

Reason (R): Transition metals have more protons in their nucleus and a more stable electronic configuration compared to alkali metals.

Answer: (1)
Explanation: Transition metals have more protons, a higher nuclear charge, and a more stable electron configuration compared to alkali metals, which results in higher ionization enthalpy.

23. Assertion (A): The density of elements in the f-block is generally higher than that of the d-block elements.

Reason (R): The large number of electrons in the f-block elements causes a stronger nuclear attraction, leading to a higher density.

Answer: (1)
Explanation: The f-block elements have a greater number of electrons, which leads to a higher nuclear charge, and consequently, a higher density than the d-block elements.

24. Assertion (A): Silver (Ag) is a typical d-block element.

Reason (R): Silver has a partially filled d-orbital and exhibits typical transition metal properties such as high conductivity and the formation of complex ions.

Answer: (1)
Explanation: Silver, like other d-block elements, has a partially filled d-orbital and exhibits typical transition metal characteristics such as high conductivity and the ability to form complex ions.

25. Assertion (A): Lanthanides are highly electropositive.

Reason (R): Lanthanides have a small atomic size and low ionization enthalpy, which makes them highly electropositive.

Answer: (1)
Explanation: Lanthanides are electropositive due to their small atomic size and low ionization enthalpy, which makes it easier for them to lose electrons.

26. Assertion (A): The transition metals form colored compounds in solution.

Reason (R): The color of transition metal compounds in solution arises from the d-d transitions between different energy levels.

Answer: (1)
Explanation: The presence of unpaired electrons in the d-orbitals of transition metals allows for d-d transitions, which result in the absorption of specific wavelengths of light and the formation of colored solutions.

27. Assertion (A): Actinides show higher oxidation states than lanthanides.

Reason (R): Actinides have a greater ability to lose electrons due to the higher nuclear charge and the poor shielding by f-electrons.

Answer: (1)
Explanation: Actinides can show higher oxidation states due to their higher nuclear charge and poor shielding of the f-electrons, which makes it easier for them to lose electrons.

28. Assertion (A): Transition metals often form complexes with ligands.

Reason (R): Transition metals have a high tendency to form coordination bonds because of their partially filled d-orbitals.

Answer: (1)
Explanation: Transition metals readily form coordination compounds with ligands due to the availability of partially filled d-orbitals that can accept electron pairs from the ligands.

29. Assertion (A): The electronic configuration of Mn²⁺ is [Ar] 3d⁵.

Reason (R): The removal of two electrons from the 4s orbital in Mn results in a stable half-filled d-subshell.

Answer: (1)
Explanation: The removal of two electrons from the 4s orbital in Mn leads to the stable 3d⁵ configuration in Mn²⁺.

30. Assertion (A): Zinc is often classified as a transition metal.

Reason (R): Zinc has a partially filled d-orbital in its ground state.

Answer: (4)
Explanation: Zinc has a completely filled d-orbital (3d¹⁰) and does not exhibit typical transition metal properties, such as variable oxidation states, so it is not considered a transition metal.

31. Assertion (A): All elements in the d-block form compounds in the +2 oxidation state.

Reason (R): The +2 oxidation state is the most stable state for most transition metals.

Answer: (3)
Explanation: While many transition metals form compounds in the +2 oxidation state, not all do. Some transition metals prefer higher oxidation states, such as +3 or +4.

32. Assertion (A): Chromium and manganese show the highest oxidation states among the first-row transition metals.

Reason (R): Both chromium and manganese have high ionization enthalpies, which enables them to achieve higher oxidation states.

Answer: (1)
Explanation: Chromium and manganese can achieve high oxidation states like +6 and +7 due to their ability to lose multiple electrons from the 4s and 3d orbitals.

33. Assertion (A): The transition elements have high melting points and hardness.

Reason (R): The metallic bonding in transition elements is strong due to the presence of delocalized d-electrons.

Answer: (1)
Explanation: The strong metallic bonding due to delocalized d-electrons in transition elements gives them high melting points and hardness.

34. Assertion (A): Lanthanides and actinides are often referred to as the f-block elements.

Reason (R): The f-block elements fill the 4f and 5f orbitals, which are located in the inner part of the periodic table.

Answer: (1)
Explanation: Lanthanides and actinides are known as f-block elements because they fill the 4f and 5f orbitals, which are located in the inner part of the periodic table.

35. Assertion (A): Transition metals are widely used as catalysts in industrial processes.

Reason (R): Transition metals can adopt multiple oxidation states, which allows them to facilitate the breaking and formation of bonds in catalytic reactions.

Answer: (1)
Explanation: The ability of transition metals to adopt multiple oxidation states enables them to act as catalysts by facilitating the breaking and forming of bonds during chemical reactions.

36. Assertion (A): The actinide series includes radioactive elements.

Reason (R): All actinides are unstable and undergo radioactive decay.

Answer: (1)
Explanation: All elements in the actinide series are radioactive, with most undergoing spontaneous radioactive decay.

37. Assertion (A): Many d-block elements are used in the making of alloys.

Reason (R): D-block elements are hard, have high melting points, and possess excellent mechanical properties, making them ideal for use in alloys.

Answer: (1)
Explanation: D-block elements, due to their hardness, high melting points, and excellent mechanical properties, are widely used in the production of alloys.

38. Assertion (A): The transition elements form amphoteric hydroxides.

Reason (R): The amphoteric nature of hydroxides is due to the ability of transition metals to show multiple oxidation states.

Answer: (1)
Explanation: Transition metals form amphoteric hydroxides because they can exhibit various oxidation states, which enables their hydroxides to behave as either acids or bases.

39. Assertion (A): The transition elements form coordination complexes with a variety of ligands.

Reason (R): Transition metals have a high tendency to form coordination compounds due to the availability of d-orbitals that can accept electron pairs.

Answer: (1)
Explanation: Transition metals have empty or partially filled d-orbitals, allowing them to form stable coordination complexes with a variety of ligands.

40. Assertion (A): The +3 oxidation state is common for many transition metals.

Reason (R): In the +3 oxidation state, the d-orbital is partially filled, leading to greater stability in many cases.

Answer: (1)
Explanation: The +3 oxidation state is common because it involves the loss of three electrons, leading to a stable configuration in many transition metals.

41. Assertion (A): Iron forms two stable oxidation states, +2 and +3.

Reason (R): The presence of unpaired electrons in iron’s d-orbitals allows it to adopt multiple oxidation states.

Answer: (1)
Explanation: Iron has a partially filled d-orbital, which allows it to form stable oxidation states of +2 and +3 due to its ability to lose electrons from both the 4s and 3d orbitals.

42. Assertion (A): Transition metals have high electrical conductivity.

Reason (R): The delocalized electrons in the metallic bond of transition metals allow easy flow of electricity.

Answer: (1)
Explanation: Transition metals exhibit high electrical conductivity because their delocalized electrons allow for the easy flow of electric current through the metal.

43. Assertion (A): Copper (Cu) is a transition metal.

Reason (R): Copper has a partially filled d-orbital in its ground state.

Answer: (1)
Explanation: Copper is a transition metal because it has an incomplete d-orbital in its ground state, which is a characteristic of transition elements.

44. Assertion (A): The transition metals exhibit variable oxidation states.

Reason (R): The transition metals have incomplete d-orbitals, which allow them to lose different numbers of electrons to form compounds in various oxidation states.

Answer: (1)
Explanation: Transition metals can exhibit variable oxidation states because their d-orbitals are partially filled, allowing for the loss of different numbers of electrons.

45. Assertion (A): Zinc (Zn) does not exhibit variable oxidation states.

Reason (R): Zinc has a completely filled 3d orbital and prefers to remain in the +2 oxidation state.

Answer: (1)
Explanation: Zinc typically exhibits only the +2 oxidation state because it has a stable, completely filled 3d orbital and does not readily lose additional electrons.

46. Assertion (A): Manganese (Mn) exhibits the highest oxidation state of +7 in the compound KMnO₄.

Reason (R): Manganese has a high ionization enthalpy, making it capable of losing multiple electrons.

Answer: (1)
Explanation: Manganese can exhibit a +7 oxidation state in KMnO₄, as it has a relatively low ionization enthalpy and can lose electrons from both its 4s and 3d orbitals.

47. Assertion (A): The lanthanide contraction occurs because of poor shielding by 4f-electrons.

Reason (R): The poor shielding effect leads to an increase in the effective nuclear charge experienced by the electrons in the same period.

Answer: (1)
Explanation: The lanthanide contraction is due to the poor shielding by 4f-electrons, which results in an increased effective nuclear charge, causing a decrease in atomic size.

48. Assertion (A): Actinides are generally radioactive.

Reason (R): The heavy atomic weight and instability of the actinide elements make them prone to radioactive decay.

Answer: (1)
Explanation: All actinides are radioactive due to their large atomic sizes and instability, which leads to spontaneous radioactive decay.

49. Assertion (A): Transition metals tend to form hard and strong metals.

Reason (R): The strong metallic bonds formed by delocalized d-electrons give rise to the hardness and strength of transition metals.

Answer: (1)
Explanation: Transition metals form hard and strong metals because of the strong metallic bonding provided by delocalized d-electrons, which bind the metal atoms together tightly.

50. Assertion (A): Scandium (Sc) is considered a transition metal.

Reason (R): Scandium has a partially filled 3d-orbital and exhibits typical transition metal characteristics.

Answer: (4)
Explanation: While scandium has a partially filled 3d-orbital, it does not exhibit typical transition metal characteristics, such as multiple oxidation states and the formation of colored compounds. Hence, it is not always considered a transition metal.

51. Assertion (A): Chromium shows a +6 oxidation state in Cr₂O₇²⁻.

Reason (R): Chromium has a relatively low ionization enthalpy, making it capable of losing six electrons in the +6 oxidation state.

Answer: (1)
Explanation: Chromium can exhibit a +6 oxidation state in Cr₂O₇²⁻ due to its ability to lose six electrons from its 4s and 3d orbitals, facilitated by its low ionization enthalpy.

52. Assertion (A): Copper forms a variety of oxidation states, including +1 and +2.

Reason (R): Copper has an electron configuration that allows for the loss of electrons from both its 4s and 3d orbitals, leading to different oxidation states.

Answer: (1)
Explanation: Copper exhibits multiple oxidation states, including +1 and +2, due to its ability to lose electrons from both the 4s and 3d orbitals.

53. Assertion (A): Molybdenum (Mo) and tungsten (W) show high melting points.

Reason (R): The high melting points of molybdenum and tungsten are due to the strong metallic bonds formed by their d-electrons.

Answer: (1)
Explanation: Molybdenum and tungsten have high melting points because the strong metallic bonds, which result from their delocalized d-electrons, require a large amount of energy to break.

54. Assertion (A): The transition elements form many colored compounds.

Reason (R): The color of the compounds is due to the d-d transitions between different energy levels in the partially filled d-orbitals of transition metals.

Answer: (1)
Explanation: Transition metals form many colored compounds due to the presence of unpaired electrons in their d-orbitals, which allows for d-d transitions that absorb specific wavelengths of light.

55. Assertion (A): The 3d block of elements is also called the transition series.

Reason (R): The 3d elements have partially filled d-orbitals, which is characteristic of transition metals.

Answer: (1)
Explanation: The 3d block elements are called the transition series because they have partially filled d-orbitals, which is a defining feature of transition metals.

56. Assertion (A): The lanthanide series includes elements from atomic numbers 57 to 71.

Reason (R): These elements have their electrons filling the 4f-orbitals, which is characteristic of lanthanides.

Answer: (1)
Explanation: The lanthanide series consists of elements with atomic numbers from 57 to 71, and they fill their 4f-orbitals, distinguishing them as lanthanides.

57. Assertion (A): The actinide series includes elements from atomic numbers 89 to 103.

Reason (R): The actinides fill the 5f-orbitals, which is characteristic of elements in the actinide series.

Answer: (1)
Explanation: The actinide series includes elements with atomic numbers from 89 to 103, and they fill their 5f-orbitals, making them distinct from other elements.

58. Assertion (A): Elements in the d-block have higher melting points than s-block elements.

Reason (R): The d-block elements have more delocalized electrons in their metallic bonds, which increases the strength of the bond and the melting point.

Answer: (1)
Explanation: The d-block elements have stronger metallic bonds due to delocalized d-electrons, which results in higher melting points compared to s-block elements.

59. Assertion (A): All transition metals form alloys.

Reason (R): Transition metals have similar atomic sizes and can combine with each other to form alloys with unique properties.

Answer: (1)
Explanation: Transition metals tend to form alloys because of their similar atomic sizes and the ability to mix with other metals to create materials with enhanced properties.

60. Assertion (A): The transition metals exhibit greater magnetic properties than other metals.

Reason (R): The presence of unpaired electrons in the d-orbitals of transition metals makes them paramagnetic.

Answer: (1)
Explanation: Transition metals are often paramagnetic due to the presence of unpaired electrons in their d-orbitals, leading to stronger magnetic properties compared to other metals.