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

Step 1: Check the Reason.
In the actinoid series the \(5f\), \(6d\) and \(7s\) orbitals lie very close together in energy. So the Reason is true.

Step 2: Check the Assertion.
Because these orbitals are so close, electrons can fill \(5f\) or \(6d\) in slightly different ways with little energy cost, so the configurations look irregular. So the Assertion is true.

Step 3: Link them.
The irregular filling happens precisely because the orbital energies are nearly equal.

Step 4: Decide the relation.
So the Reason is the correct explanation of the Assertion.

Step 5: Conclusion.
Both are true and the Reason correctly explains the Assertion.

Answer: Both Assertion and Reason are true and Reason is the correct explanation of the Assertion (Option 1).