Question

as you move from left to right across period 3, which statement is true of the number of valence electrons as you move from one main - group element to the next?
a. the number of valence electrons decreases by a multiple of 2.
b. the number of valence electrons decreases by 1.
c. the number of valence electrons increases by 1.
d. the number of valence electrons increases by a multiple of 2.

Explanation:

Main - group elements in a period (like Period 3) have their valence - electron count related to their group number. As we move from left to right across a period (from one main - group element to the next), the group number increases by 1. Since the number of valence electrons for main - group elements is equal to the group number (for groups 1 - 2 and 13 - 18), the number of valence electrons increases by 1.

Answer:

C. The number of valence electrons increases by 1.