Question

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

Explanation:

To solve this, we analyze periodic table trends:

1. Valence electrons trend across a period: When moving left - to - right across a period (excluding transition elements), the number of valence electrons increases by 1. For example, in period 2, Li has 1 valence electron, Be has 2, B has 3, and so on until Ne with 8.
2. Energy levels trend across a period: The number of energy levels (shells) remains the same across a period. It is the number of energy levels that increases when moving down a group. So the options about energy levels increasing or decreasing by one across a period are incorrect. And the option saying valence electrons decrease by one is also incorrect as we move left - to - right.

Answer:

B. Valence electrons increase by one.