Which element has 7 valence electrons?

• A. Sodium (Na)
• B. Oxygen (O)
• C. Chlorine (Cl)
• D. Magnesium (Mg)

Answer: (C)

Verified step by step guidance

1. Understand that valence electrons are the electrons in the outermost shell of an atom and determine the chemical properties of the element.
2. Recall that elements in the same group (column) of the periodic table have the same number of valence electrons.
3. Identify the group number of each element: Sodium (Na) is in Group 1, Oxygen (O) is in Group 16, Chlorine (Cl) is in Group 17, and Magnesium (Mg) is in Group 2.
4. Know that Group 17 elements, also called halogens, have 7 valence electrons.
5. Therefore, the element with 7 valence electrons among the options is the one in Group 17, which is Chlorine (Cl).