Question

what does the group number for representative elements indicate?
number of protons
number of energy levels
mass number
number of valence electrons

Explanation:

To determine the correct answer, we analyze each option:

• "Number of protons" is the atomic number, not related to group number.
• "Number of energy levels" is related to the period number, not group number.
• "Mass number" is protons + neutrons, unrelated to group number.
• For representative elements (main - group elements), the group number is equal to the number of valence electrons. For example, Group 1 elements have 1 valence electron, Group 2 has 2, and Groups 13 - 18 have valence electrons equal to group number - 10 (e.g., Group 17 has 7 valence electrons).

Answer:

D. Number of valence electrons