$MgO$ is used as a refractory material because

$Beryllium$ shows a diagonal relationship with:

Identify the correct statements from the following.
$(A)$ $BeSO_4$ is soluble in water.
$(B)$ $BeO$ is an amphoteric oxide.
$(C)$ $CO$ can be obtained by heating $CaCO_3$ at $1070-1270 \ K$.

The hydroxide of which of the following metals reacts with both acid and alkali?

$X$-ray tube windows are made using which of the following metals?

The correct order of decomposition temperature of $MgCO_3$ $(X)$,$BaCO_3$ $(Y)$,$CaCO_3$ $(Z)$ is