Question

select the correct answer.
which of these pairs of elements have the same number of valence electrons?
a. oxygen (o) and bromine (br)
b. selenium (se) and bromine (br)
c. carbon (c) and lead (pb)
d. oxygen (o) and carbon (c)
e. sodium (na) and magnesium (mg)

Explanation:

Step1: Recall valence electrons and groups

Elements in the same group of the periodic table have the same number of valence electrons. Let's identify the group of each element:

• Oxygen (O) is in Group 16, so valence electrons = 6.
• Bromine (Br) is in Group 17, valence electrons = 7.
• Selenium (Se) is in Group 16, valence electrons = 6.
• Carbon (C) and Lead (Pb) are in Group 14, valence electrons = 4.
• Sodium (Na) is in Group 1, valence electrons = 1.
• Magnesium (Mg) is in Group 2, valence electrons = 2.

Step2: Analyze each option

• Option A: O (6) and Br (7) → different.
• Option B: Se (6) and Br (7) → different.
• Option C: C (4) and Pb (4) → same (both Group 14).
• Option D: O (6) and C (4) → different.
• Option E: Na (1) and Mg (2) → different.

Answer:

C. carbon (C) and lead (Pb)