Which of the following is a use of alum?

Explain the following:
$(1)$ $BF_3$ does not hydrolyze.
$(2)$ Why does the element silicon not form a graphite-like structure,whereas carbon does?

$A$. What are silicones? State the uses of silicones.
$B$. What are boranes? Give chemical equation for the preparation of diborane.

Boron halides behave as Lewis acids because of their nature.

Which of the following elements is used in thermometry at high temperatures?

Which of the following is the correct match?