ANSWER
Step-by-step explanation
Firstly, we need to state the periodic law
Periodic law states that elements are in their periodic function of their atomic number. This implies that elements are arranged in the periodic table based on their atomic table
Recall, that the periodic table is divided into groups and periods. The groups tell us the chemical properties of the element and the number of valence electrons each element have.
Recall, that valency is the combining power of an element.
So, all elements in group 1 has a valence electron of 1
All elements in group 2 will have a valence electrons of 2
All elements in group 3 will have a valence electrons of 3