Question

Assertion (A): Actinoids show irregularities in their electronic configurations.
Reason (R): In actinoids 5f, 6d and 7s orbitals are of comparable energies.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

In the actinoid series the 5f, 6d and 7s orbitals lie very close together in energy, so the Reason is true.

Answer 1

The Correct Option is A

Concept: In the actinoid series the 5f, 6d and 7s orbitals lie very close together in energy, so the Reason is true. Because these orbitals are so close in energy, electrons can occupy 5f or 6d in different ways with little energy difference, which leads to irregularities in the electronic configurations of the actinoids, so the Assertion is true. The comparable energies of these orbitals are exactly the cause of the irregular configurations, so the Reason correctly explains the Assertion.
Answer: Option (A) - both A and R are true and R is the correct explanation of A, because the close energies of 5f, 6d and 7s orbitals are the reason for the irregular configurations.