Give suitable laboratory preparation for diborane.

Describe the shapes of $BF_3$ and $BH_4^-$. Assign the hybridisation of boron in these species.

Heating an aqueous solution of aluminium chloride to dryness will give:

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

Assertion $A$ : The stability order of +$1$ oxidation state of $\mathrm{Ga}$, In and $\mathrm{Tl}$ is $\mathrm{Ga}<\mathrm{In}<\mathrm{Tl}$.

Reason $R$ : The inert pair effect stabilizes the lower oxidation state down the group.

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

The element which exists in liquid state for a wide range of temperature and can be used for measuring high temperature is :-