 # Given below are two statements :one is labelled as Assertion A and the other `
Question:

Given below are two statements :one is labelled as Assertion A and the other is labelled as Reason R

Assertion $\mathbf{A}:$ In $\mathrm{T} \ell \mathrm{I}_{3}$, isomorphous to $\mathrm{CsI}_{3}$, the metal is present in $+1$ oxidation state.

Reason R : T $\ell$ metal has fourteen $\mathrm{f}$ electrons in the electronic configuration.

In the light of the above statements, choose the most appropriate answer from the options given below:

1. $\mathbf{A}$ is correct but $\mathbf{R}$ is not correct

2. Both $\mathbf{A}$ and $\mathbf{R}$ are correct and $\mathbf{R}$ is the correct explanation of $\mathbf{A}$.

3. A is not correct but $\mathbf{R}$ is correct

4. Both $\mathbf{A}$ and $\mathbf{R}$ are correct but $\mathbf{R}$ is NOT the correct explanation of $\mathbf{A}$.

Correct Option: , 4

Solution:

$\mathrm{T} \ell \mathrm{I}_{3} \Rightarrow\left(\mathrm{T} \ell^{\oplus} \& \mathrm{I}_{3}^{\ominus}\right)$

$\mathrm{CsI}_{3} \Rightarrow\left(\mathrm{Cs}^{\oplus} \& \mathrm{I}_{3}^{\ominus}\right)$

[Both have same crystalline structure is called isomorphous]

$\mathrm{T} \ell_{(81)}^{\oplus}=\left[\mathrm{Xe}_{54}\right] 4 \mathrm{f}^{14}, 5 \mathrm{~d}^{10}, 6 \mathrm{~s}^{2}$

(It is correct due to present 14 f electrons in $\mathrm{T} \ell^{\oplus}$ ion)