The correct order of basic strength of oxides of alkaline earth metals is:

The commercial name for calcium oxide is

Which of the following elements does not exhibit variable valency?

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 $1070-1270 \ K$.

Complete the following equation: $CaCO_3 \cdot MgCO_{3(s)} \xrightarrow{\Delta }$

$A$ 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