Which of the following on thermal decomposition gives both basic and acidic oxides?

$A$ solid compound $X$ on heating gives $CO_2$ gas and a residue. The residue mixed with water forms $Y$. On passing an excess of $CO_2$ through $Y$ in water,a clear solution $Z$ is obtained. On boiling $Z$,compound $X$ is reformed. The compound $X$ is

Which of the following does not react with cold or hot water?

$Assertion$ $(A)$: Helium and beryllium have similar outer electronic configuration $ns^2$. $Reason$ $(R)$: Both are chemically inert.

Select the incorrect statement about alkaline earth metals.

Why is beryllium amphoteric in nature?