Ionisation energy is a measure of the amount of energy required to remove an outer electron from an atom creating a positively charged ion.
The Group 2 Alkaline earth metals are the 2nd group in the periodic table and are just before the transition metals. They are all similar in their color of silvery/white metals and react with water to form alkaline solutions. They are however not as reactive as the group 1 metals as they have 2 valence electrons instead of 1.
Group 18 the Noble Gases are the name given to a collection of gases that exist in Group 18 at the very end of the periodic table. They are all non metals and exist as monoatomic gases which are relatively inert and unreactive due to their full outer shell of electrons.