Which pair of metals is present in dolomite?

Which of the following statements is $\text{Incorrect}$:

$A$ metal $M$ readily gives $MSO_4$, which is soluble in water. It forms its oxide $MO$ which is amphoteric. It forms an insoluble hydroxide $M(OH)_2$, which is soluble in $NaOH$ solution. The $M$ is

$A$ compound $X$ on heating gives a colourless gas. The residue is dissolved in water to obtain $Y$. Excess $CO_2$ is bubbled through the aqueous solution of $Y$ and $Z$ is formed. $Z$ on gentle heating gives back $X$. The compound $X$ is:

Which of the following elements does not exhibit variable valency?

Statement $A$: Calcium chloride $(CaCl_2)$ is not useful for drying alcohols or $NH_3$.
Reason $R$: $CaCl_2$ is not a good desiccant.