Question

atomic size generally
remains constant within a period.
decreases as you move from left to right across a period.
decreases as you move from top to bottom within a group.
increases as you move from left to right across a period.

Explanation:

As we move from left to right across a period in the periodic table, the number of protons in the nucleus increases. This leads to a greater positive charge in the nucleus, which attracts the electrons more strongly. As a result, the atomic size (atomic radius) decreases.

Answer:

decreases as you move from left to right across a period.