Which of the following elements has 7 valence electrons?

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

Answer: (A)

Verified step by step guidance

1. Recall that the number of valence electrons corresponds to the electrons in the outermost shell of an atom, which determines its chemical properties.
2. Identify the group number of each element in the periodic table, as elements in the same group have the same number of valence electrons.
3. Sodium (Na) is in Group 1, so it has 1 valence electron.
4. Oxygen (O) is in Group 16, so it has 6 valence electrons.
5. Chlorine (Cl) is in Group 17, so it has 7 valence electrons, which matches the question's requirement.