Identify the incorrect reaction.

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 $Ba^{2+}$.

An element reacts with hydrogen to form a compound $A$,which on treatment with water liberates hydrogen gas. The element can be

In the hardening stage of Plaster of Paris,the compound formed is:

What happens when:
$(i)$ magnesium is burnt in air
$(ii)$ quick lime is heated with silica
$(iii)$ chlorine reacts with slaked lime
$(iv)$ calcium nitrate is heated?

Thermal stability of $MCO_3$ is in order: