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The main reason for larger number of oxidation states exhibited by the actinoids than the corresponding lanthanoids, is :-
A
Lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals
B
More energy difference between 5f and 6d orbitals than between 4f and 5d orbitals
C
Greater reactive nature of the actinoids than the lanthanoids
D
Larger atomic size of actinoids than the lanthanoids
Detailed Solution
Lanthanoids show mainly the +3 oxidation state, while actinoids show a wide range of oxidation states, from +3 up to +7.
In actinoids the 5f, 6d and 7s orbitals are of comparable energies; the energy gap between 5f and 6d is small.
So electrons from all these orbitals can take part in bonding, and many oxidation states are possible.
In lanthanoids the 4f orbitals lie deeper (they are well shielded) and the gap between 4f and 5d is larger, so the 4f electrons are not easily used in bonding.
So the main reason is the lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals.
In actinoids the 5f, 6d and 7s orbitals are of comparable energies; the energy gap between 5f and 6d is small.
So electrons from all these orbitals can take part in bonding, and many oxidation states are possible.
In lanthanoids the 4f orbitals lie deeper (they are well shielded) and the gap between 4f and 5d is larger, so the 4f electrons are not easily used in bonding.
So the main reason is the lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals.