* Group IIA (Group 2): Elements in Group IIA have 2 valence electrons.

* 18 Electrons: This tells us the cation has lost electrons.

Finding the Element:

* Neutral Atom: To have 18 electrons after losing some, the neutral atom must have started with 20 electrons.

* Atomic Number: The number of electrons in a neutral atom is equal to its atomic number. So, the element has an atomic number of 20.

* Element: The element with atomic number 20 is Calcium (Ca).

The Cation:

Calcium loses its two valence electrons to form a +2 cation: Ca²⁺