A: Lanthanoids have +3 as most common
oxidation state. R: Electrons of 4f in lanthanoids rarely participate

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If Assertion and rason both are false statement then mark (4)

Answer

To solve the question regarding the assertion and reason about lanthanoids, we will break down the concepts step by step.

### Step 1: Understanding the Assertion
**Assertion (A)**: Lanthanoids have +3 as the most common oxidation state.

- **Explanation**: The lanthanoids, which are the 15 elements from lanthanum (La) to lutetium (Lu), predominantly exhibit a +3 oxidation state. This is because they typically lose three electrons when they form compounds. The electrons lost are from the outermost 6s subshell and one from the 4f subshell.

### Step 2: Understanding the Reason
**Reason (R)**: Electrons of 4f in lanthanoids rarely participate in bonding.

- **Explanation**: The 4f electrons are located deeper in the electron shell and are strongly shielded by the outer 5s and 5p electrons. This shielding effect makes it energetically unfavorable for the 4f electrons to participate in bonding, which is why they are not typically involved in forming oxidation states other than +3.

### Step 3: Analyzing the Relationship
- Both the assertion and reason are correct. The reason provides a valid explanation for the assertion. The +3 oxidation state is common because the 4f electrons are not easily removed due to their energy levels and shielding.

### Conclusion
Both the assertion and reason are correct, and the reason correctly explains the assertion. Therefore, the correct answer is that both A and R are true, and R is the correct explanation of A.

### Final Answer
Both the assertion and reason are correct, and the reason is the correct explanation for the assertion.

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