A metal $\left(X\right)$ dissolves both in dilute $HCl$ and dilute $NaOH$ to liberate $H_2.$ Addition of $N{H}_{4}Cl$ and excess $N{H}_{4}OH$ to an $HCl$ solution of $X$ produces $Y$ as a precipitate. $Y$ is also produced by adding $N{H}_{4}Cl$ to the $NaOH$ solution of $X.$ The species $X$ and $Y,$ respectively, are

Given below are two statements: one is labelled as Assertion $\mathrm{A}$ and the other is labelled as Reason $\mathrm{R}$.

Assertion $\mathrm{A}:$ In $\mathrm{T}l{\mathrm{I}}_3,$ isomorphous to ${\mathrm{CsI}}_3$, the metal is present in $+1$ oxidation state.

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

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

Given below are two statements: one is labelled as Assertion $\mathrm{A}$ and the other is labelled as Reason $\mathrm{R}$

Assertion $\mathrm{A}$: Boron is unable to form ${\mathrm{BF}}_6^{3-}$

Reason $\mathrm{R}$: Size of $\mathrm{B}$ is very small.

In the light of the above statements, choose the correct answer from the options given below

Identify the correct statements about the anomalous behaviour of Boron

I. Boron trihalides can form dimeric structures.

II. Boron shows $+1$ as stable oxidation state

III. Maximum covalency of Boron is four.

IV. Boron does not form ${\mathrm{BF}}_6^{6-}$ ion.