Question

when moving across a period from left to right in the periodic table (excluding transition elements) which trend occurs? (1 point)
the energy levels increase by one
valence electrons decrease by one
valence electrons increase by one
the energy levels decrease by one

Explanation:

Elements in the same period have the same number of electron energy levels. As you move left to right across a period (excluding transition elements), each subsequent element has one more proton and one more electron, so the number of valence electrons increases by one per element.

Answer:

Valence electrons increase by one