To determine which element has four valence electrons, we should examine the electron configurations of each element. The valence electrons are found in the outermost shell of an atom.
A. Hafnium (Hf): Hafnium is located in group 4 and period 6 of the periodic table. Its electron configuration is [Xe] 4f^14 5d^2 6s^2. Even though hafnium has two electrons in its 6s sublevel, it does not have four valence electrons.
B. Radon (Rn): Radon is located in group 18 and period 6 of the periodic table. It is a noble gas with a full outer shell. Its electron configuration is [Xe] 4f^14 5d^10 6s^2 6p^6, giving it a total of 8 valence electrons, not four.
C. Silicon (Si): Silicon is located in group 14 and period 3 of the periodic table. Its electron configuration is [Ne] 3s^2 3p^2. In its outermost shell, silicon has a total of four valence electrons (2 in the 3s sublevel and 2 in the 3p sublevel).
D. Sulfur (S): Sulfur is located in group 16 and period 3 of the periodic table. Its electron configuration is [Ne] 3s^2 3p^4. It has a total of six valence electrons.
Based on the electron configurations and the number of valence electrons:
The correct answer is C. silicon (Si).
