Alkali metals are elements found in Group 1 of the periodic table. These metals are characterized by having one electron in their outermost shell.
- Sodium (Na) is an alkali metal as it is in Group 1 of the periodic table.
- Calcium (Ca) and Magnesium (Mg) are alkaline earth metals, found in Group 2.
- Aluminum (Al) is a post-transition metal and is found in Group 13.
Therefore, the correct answer is option (A).