Question:
Given below are two statements
Statement-I:
Due to lanthanoid contraction 4d- and 5d-series of elements have more or less same atomic and ionic radii
Statement-II:
Lanthanoids exhibit more number of oxidation states than actinoids
Given below are two statements
Statement-I:
Due to lanthanoid contraction 4d- and 5d-series of elements have more or less same atomic and ionic radii
Statement-II:
Lanthanoids exhibit more number of oxidation states than actinoids
Show Hint
Lanthanoids:
Mostly +3 oxidation state.
Actinoids:
Show many oxidation states (+3 to +7 commonly).
Hence actinoids have greater oxidation-state variability.
Updated On: Jun 22, 2026
- Both statements I and II are correct
- Statement I is correct but statement II is not correct
- Statement I is not correct but statement II is correct
- Both statements I and II are not correct \bigskip
Show Solution
Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Concept:
Lanthanoid contraction refers to the gradual decrease in atomic and ionic radii across the lanthanoid series due to poor shielding by 4f electrons.
Step 1: Examine Statement-I carefully.
Because of lanthanoid contraction, the size of 5d elements becomes nearly equal to that of corresponding 4d elements. Examples: \[ Zr \approx Hf \] \[ Nb \approx Ta \] Thus Statement-I is correct.
Step 2: Examine Statement-II carefully.
Actinoids show a larger number of oxidation states because 5f, 6d and 7s orbitals have comparable energies. Examples: \[ U(+3,+4,+5,+6) \] \[ Np(+3,+4,+5,+6,+7) \] \[ Pu(+3,+4,+5,+6,+7) \] Lanthanoids predominantly show \[ +3 \] oxidation state with only a few exceptions. Therefore actinoids exhibit more variable oxidation states than lanthanoids. \[ \text{Statement-II is false} \]
Step 3: Final conclusion.
Statement-I is true. Statement-II is false. Hence the correct option is \[ \boxed{\text{Statement I is correct but Statement II is not correct}} \]
Step 1: Examine Statement-I carefully.
Because of lanthanoid contraction, the size of 5d elements becomes nearly equal to that of corresponding 4d elements. Examples: \[ Zr \approx Hf \] \[ Nb \approx Ta \] Thus Statement-I is correct.
Step 2: Examine Statement-II carefully.
Actinoids show a larger number of oxidation states because 5f, 6d and 7s orbitals have comparable energies. Examples: \[ U(+3,+4,+5,+6) \] \[ Np(+3,+4,+5,+6,+7) \] \[ Pu(+3,+4,+5,+6,+7) \] Lanthanoids predominantly show \[ +3 \] oxidation state with only a few exceptions. Therefore actinoids exhibit more variable oxidation states than lanthanoids. \[ \text{Statement-II is false} \]
Step 3: Final conclusion.
Statement-I is true. Statement-II is false. Hence the correct option is \[ \boxed{\text{Statement I is correct but Statement II is not correct}} \]
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