Which among the following elements of group-$2$ exhibits anomalous properties?

Which of the following elements is chemically most reactive?

Pure anhydrous $MgCl_2$ can be prepared from the hydrated salt by

How would you explain the following observations?
$(i)$ $BeO$ is almost insoluble but $BeSO_4$ is soluble in water,
$(ii)$ $BaO$ is soluble but $BaSO_4$ is insoluble in water,
$(iii)$ $LiI$ is more soluble than $KI$ in ethanol.

Which of the following orders is correct $:-$

The thermal stability of $MCO_3$ (where $M$ is an alkaline earth metal) follows the order: