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

Sodium borohydride upon treatment with iodine produces a Lewis acid $(X)$,which on heating with ammonia produces a cyclic compound $(Y)$ and a colourless gas $(Z)$. $X, Y$ and $Z$ are $....$

The incorrect statement regarding $X$ in the given reaction is:
$BF_3 + LiAlH_4 \xrightarrow{\text{Ether}} X + LiF + AlF_3$

Diborane reacts with ammonia under different conditions to give a variety of products. Which one among the following is not formed in these reactions?

Which one among the following statements is correct about a solution of borax in water?

Two elements $X$ and $Y$ react with highly electropositive metals to form binary compounds,which upon hydrolysis yield borane and silane,respectively. What are $X$ and $Y$?