In which of the following,a salt of the type $KMO_2$ is obtained?

Which of the following is a use of alum?

$H_3BO_3$ $\xrightarrow{T_1} X$ $\xrightarrow{T_2} Y$ $\xrightarrow{\text{red hot}} B_2O_3$
If $T_1 < T_2$,then $X$ and $Y$ respectively are:

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:

Which of the following chlorides does not react with $PCl_5$ on heating?

Which metal is protected by a layer of its own oxide?