What is the main similarity among elements in group 2?

             Chemical Properties

Explanation:
                   Elements belonging to same group in a periodic table have same chemical properties. This similarity in chemical properties arises mainly from the same number of valence shell electrons. Group 2 elements also called Alkaline Earth Metals have two valence electrons in their valence shell with following electronic configuration

                                                       ns²

Where "n" represents principle quantum number or number of main shell.

The reactivity of these elements is due to the metallic behavior as these elements looses two electrons to form a cation with +2 oxidation number. i.e.

                                          X   →   X⁺²  +  2 e⁻

Therefore, all elements present on Group II will form a cation with +2 oxidation number and behave in the same manner with different reagents.

You would be correct, boiling water does disinfect contamination.    the property of disinfecting means to kill  germs, bacteria and other pathogens or contamination  that might cause an infection or cause a person to become sickly. a couple methods of disinfecting are using soap, other cleaning supplies or by simply "boiling" the contaminate.  the reason why boiling water disinfects certain attributes is because some cells cannot survive the heat and pressure.