Question

atomic size generally

decreases as you move from top to bottom within a group.

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

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

remains constant within a period.

Explanation:

Atomic size trends:

• Down a group: As you move from top to bottom within a group, atomic size increases. This is because new electron shells are added, increasing the distance from the nucleus to the outermost electrons.
• Across a period: As you move from left to right across a period, the number of protons in the nucleus increases (increasing the nuclear charge), while the electrons are added to the same shell. The increased nuclear charge pulls the electrons closer, so atomic size decreases.

Answer:

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