Here's why:

* Valence electrons are the electrons in the outermost shell of an atom. They are the ones involved in chemical bonding.

* Group 2 elements (also called alkaline earth metals) are located in the second column of the periodic table.

* Their electron configuration typically ends with an ns² configuration, where 'n' is the principal quantum number of the outermost shell. This means they have two electrons in their outermost shell.

For example:

* Beryllium (Be) has an electron configuration of 1s²2s². It has 2 valence electrons in the 2s orbital.

* Magnesium (Mg) has an electron configuration of 1s²2s²2p⁶3s². It has 2 valence electrons in the 3s orbital.