Given below are two statements :one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : In $\mathrm{T} \ell I_3$, isomorphous to $\mathrm{CsI}_3$, 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: