Explain why hydrated magnesium chloride can not be dehydrated upon heating.

The hydrated halides of ____ cannot be dehydrated on heating.

From hydrated magnesium chloride, anhydrous magnesium chloride can be prepared by heating the hexahydrate in :

Anhydrous magnesium chloride can be prepared by heating MgCl_(2)6H_(2)O

The main source of magnesium chloride is

Why hydrated chlorides of Ca, Sr and Ba can be dehydrated by heating while those of Be and Mg suffer hydrolysis?