* Valence Electrons: Valence electrons are the electrons in the outermost shell of an atom. These electrons are involved in chemical bonding.

* Electron Configuration:

* Carbon (C): 2-4 (has 4 valence electrons)

* Aluminum (Al): 2-8-3 (has 3 valence electrons)

* Sodium (Na): 2-8-1 (has 1 valence electron)

* Calcium (Ca): 2-8-8-2 (has 2 valence electrons)

Therefore, only Aluminum has three electrons in its valence shell.