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. the energy levels decrease by one. valence electrons increase by one. valence electrons decrease by one.

Explanation:

As we move from left - right across a period (excluding transition elements) in the periodic table, the number of protons in the nucleus increases. This leads to an increase in the effective nuclear charge. As a result, the number of valence electrons increases by one successively for each element moving across the period. Energy levels do not change across a period; they are determined by the principal quantum number which remains the same within a period.

Answer:

Valence electrons increase by one.