Region A ⇒ group 2
Further explanation
Valence electrons are electrons used in a chemical bond , and in an atom's outermost energy level
The periodic system of elements is an arrangement of elements classified based on similar properties and their atomic number order.
The periodic system is divided into groups (vertical order) and periods (horizontal order)
In the periodic system
The group number in the periodic system is determined by the same valence electrons (main group), while the period is determined by the number of shells
The 2 valence electrons are in group 2
A : group 2 : Valence electrons =2
B: group 13 : Valence electrons = 3
C : group 15 : Valence electrons = 5
D : group 16 : Valence electrons = 6
