Highest melting point among the following is displayed by

Identify correct statements from the following:
$i$. Beryllium oxide is an amphoteric oxide.
$ii$. Group $II$ elements dissolve in liquid ammonia to form deep blue-black solutions.
$iii$. The hydration enthalpy of group $II$ ions decreases from $Be^{2+}$ to $Ba^{2+}$.

$A$ 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 are amphoteric oxides?

$A$ 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 is not correct?