Milk of magnesia 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:

Identify the option in which the trends corresponding to hydroxides of group $2$ elements (from $Mg(OH)_2$ to $Ba(OH)_2$) are correctly shown:

Basic character

Chemical stability

Solubility

Which element from the following is used for cancer treatment?

Mortar is a mixture of which of the following?

$A$ metal $M$ readily forms a water-soluble sulfate $MSO_4$,a water-insoluble hydroxide $M(OH)_2$,and an oxide $MO$ which becomes inert upon heating. The hydroxide is soluble in $NaOH$. What is $M$?