Which of the following metals belong to the same group in the periodic table?

Group $2$ hydrides with significant covalent character is/are:

Which of the following has the highest basic nature?

Describe the importance of the following:
$(i)$ limestone
$(ii)$ cement
$(iii)$ plaster of Paris.

$A$ chemistry student wants to identify the metal ion in a salt. They make a paste of the salt with concentrated $HCl$ on a clean platinum wire loop. If they take a small amount of this paste and place it in a non-luminous flame,it produces a green flame. Which metal is present?

$BeF_2$ is soluble in water,whereas the fluorides of other alkaline earth metals are insoluble. The reason for this is .......