Solubility of sulphates of group $2$ elements decreases down the group due to

What is slaking of lime?

Which one of the following is fluorspar?

The halides of alkaline earth metals form hydrates such as $MgCl_2 \cdot 6H_2O$,$CaCl_2 \cdot 6H_2O$,$BaCl_2 \cdot 2H_2O$,and $SrCl_2 \cdot 2H_2O$. What does this indicate about the halides of group $2$ elements?

An element has an atomic number of $56$. To which of the following categories does it belong?

The hydroxides which sublime on heating are