Question

The main reason for larger number of
oxidation states exhibited by the actinoids
than the corresponding lanthanoids, is
(a) more energy difference between 5f and
6d orbitals than between 4f and 5d orbitals.
(b) lesser energy difference between 5f and
6d orbitals than between 4f and 5d orbitals.
(c) larger atomic size of actinoids than the
lanthanoids.
(d) greater reactive nature of the actinoids
than the lanthanoids.

Answer 1

the lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals

Actinoids shows larger oxidation states due to poor shielding of both  4f and  5f orbital electrons as a result these orbital have almost similar energy and hence take part in bond formation. Also, there is very small energy between  5f,6d and 7s subshells.

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