* Ionic Size Trends: Ionic size generally increases as you move down a group (column) on the periodic table and decreases as you move across a period (row).

* Arsenic (As) and Bromine (Br): Arsenic is in Group 15, and bromine is in Group 17. This means arsenic is further down the periodic table than bromine.

Therefore, an arsenic ion (As³⁻) is larger than a bromine ion (Br⁻).

Explanation:

* Moving down a group, the number of electron shells increases, leading to larger atomic and ionic radii.

* Moving across a period, the number of protons in the nucleus increases, attracting the electrons more strongly and resulting in a smaller atomic and ionic radii.