The element having atomic number $56$ belongs to

Heating compound $(A)$ produces a colorless gas and a residue $(B)$ which dissolves in water. Passing excess $CO_2$ gas through the aqueous solution of $(B)$ yields compound $(C)$,which is obtained in solid state. Gently heating compound $(C)$ gives back the white solid $(A)$. What is compound $(A)$?

Alkaline earth metals are denser than alkali metals,because metallic bonding in alkaline earth metals is:

When $CO_2$ is passed into lime water,it turns milky. When an excess of $CO_2$ is passed,the milkiness disappears because:

$A$ solid compound $X$ on heating gives $CO_2$ gas and a residue. The residue mixed with water forms compound $Y$. On passing excess $CO_2$ gas through $Y$,a clear solution $Z$ is formed. On heating $Z$,compound $X$ is recovered. What is compound $X$?
$\mathop X\limits_{solid}$ $\xrightarrow{\text{heating}} CO_2 + \text{residue}$ $\xrightarrow{H_2O} Y$ $\xrightarrow{\text{excess } CO_2} \mathop Z\limits_{\text{solution}}$ $\xrightarrow{\text{heating}} X$

Beryllium shows a diagonal relationship with aluminum. Which of the following similarities is incorrect?