WAEC Chemistry 2023 Paper

Concept:The valence electron is the electron in the outermost shell, and its orbital type can be found from the electron configuration.Explanation:Sodium has atomic number $11$, so it has $11$ electrons.Its electron configuration is $1s^2\,2s^2\,2p^6\,3s^1$.The outermost shell is the third shell, and the valence electron is in the $3s$ orbital.The $3s$ orbital is an s-orbital, so sodium has its valence electron in the s-orbital.Aluminum, phosphorus, and carbon have valence electrons in p-orbitals as well.Answer:C. Sodium