Given below are two statements one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : In `TlI_(3)`, isomorphous to `CsI_(3)` the metal is present in +1 oxidation state.
Reason R: Tl metal has fourteen f electrons in the electronic configuration.
In the light of the above statements, choose the most appropriate answer from the options given below:

Options

A. A is correct but R is not correct
B. Both A and R are correct and R is the correct explanation of A.
C. A is not correct but R is correct
D. Both A and R are correct but R is NOT the correct explanation of A.

Answer

To solve the given question, we need to analyze the Assertion (A) and Reason (R) statements regarding thallium (Tl) and cesium (Cs).

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that in TlI₃, which is isomorphous to CsI₃, the metal thallium is present in the +1 oxidation state.
- To verify this, we need to consider the oxidation states of thallium in its compounds. Thallium can exhibit +1 and +3 oxidation states, but in TlI₃, the +1 state is indeed more stable due to the inert pair effect.

2. **Understanding the Reason (R)**:
- The reason states that thallium metal has fourteen f electrons in its electronic configuration.
- The electronic configuration of thallium (atomic number 81) is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹. This confirms that thallium has 14 f electrons, specifically in the 4f subshell.

3. **Evaluating the Relationship Between A and R**:
- The assertion is true because thallium does exist in the +1 oxidation state in TlI₃.
- The reason is also true as thallium indeed has 14 f electrons.
- Furthermore, the reason provides a correct explanation for the assertion. The inert pair effect, which arises due to the presence of f electrons, leads to the stability of the +1 oxidation state over the +3 state in thallium.

4. **Conclusion**:
- Both the assertion and the reason are true, and the reason is the correct explanation for the assertion.

### Final Answer:
The correct answer is: **Both Assertion A and Reason R are true, and R is the correct explanation of A.**

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