Aluminium is not used:

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

Give the physical and chemical properties of orthoboric acid $(H_3BO_3)$.

The correct order of Lewis acidity for $BX_3$ is:

Boron trifluoride on reaction with lithium aluminium hydride in ether gives $LiF$, $AlF_3$ and $X$. $X$ on reaction with $NH_3$ gives $Y$. $Y$ on further heating gives a compound $Z$. The number of $\sigma$-bonds and $\pi$-bonds in $Z$ are $x$ and $y$ respectively. $(x+y)$ is equal to

Borazine,also known as inorganic benzene,can be prepared by the reaction of $3$ equivalents of "$X$" with $6$ equivalents of "$Y$". "$X$" and "$Y$",respectively,are: