Which of the following compounds of boron does not exist in the free form

For compound having the formula $GaAlCl _4$, the correct option from the following is

Below are two statements, one labeled as Assertion $(A)$ and the other as Reason $(R):$

Assertion $(A)$: Among group $13$ elements, boron's melting point is unusually high $(2453 \mathrm{~K})$.

Reason $(R):$ Solid boron has a strong crystalline lattice.

In the context of the above statements, choose the correct answer from the following options:

In the purification of bauxite by Hall's process

Which one is used as a bye-product in Serpeck's process

Which of the following compound does not show the amphoteric behaviour