Which of the following elements has its valence electrons in the s-orbital?

Explanation

Sodium is an alkali metal, and its atomic number is 11. This means that it has 11 electrons, and its electron configuration is \(1s^2 2s^2 2p^6 3s^1\). The valence electrons are the electrons in the outermost shell, which in this case is the 3s orbital.