Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: In $T \ell I_{3}$,isomorphous to $CsI_{3}$,the metal is present in $+1$ oxidation state.
Reason $R$: $T \ell$ 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:

• 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 $A$.