Answer:
As you move from left to right across a period,the number of valence electrons increases.
Step-by-step explanation:
The horizontal rows of the periodic table are called periods. The elements that form the same row, have different properties but similar masses: each element is placed according to its electronic configuration. The period that an element occupies coincides with its last electronic layer, therefore an element with five electronic layers, will be located in the fifth period.
When you move from left to right in the same period, the number of the group to which the atomic element belongs is increased. The group determines the number of electrons in its last layer (valance electrons). Then, if the group number is increased, the amount of electrons in the last layer increases.
So, you can say that as you move from right to left across a period, the number of valence electrons increises.