* Valence Electrons: These are the electrons in the outermost energy level of an atom, and they are the ones involved in chemical bonding.

* Electron Configuration: To find valence electrons, you need to know the element's electron configuration.

Let's look at each option:

* Silicon (Si): Electron configuration: 2, 8, 4. Silicon has 4 valence electrons.

* Lithium (Li): Electron configuration: 2, 1. Lithium has 1 valence electron.

* Magnesium (Mg): Electron configuration: 2, 8, 2. Magnesium has 2 valence electrons.

* Chlorine (Cl): Electron configuration: 2, 8, 7. Chlorine has 7 valence electrons.

Therefore, the answer is B. Lithium (Li) has the fewest valence electrons (1).