Which statements correctly apply the usual main-group valence-electron rule for groups 13 through 18? Select all that apply.
A group 16 main-group atom usually has 16 valence electrons.
A group 16 main-group atom usually has 6 valence electrons.✓Правильный ответ
Helium has 8 valence electrons.
Helium has 2 valence electrons.✓Правильный ответ
Объяснение
Subtracting 10 from the group number gives the usual valence count in this range, making group 16 correspond to six. Helium is the exception because its complete first shell contains two electrons rather than eight.