Question

When an atom of phosphorus becomes a phosphide ion (P3–), the radius

(1) decreases
(2) increases
(3) remains the same?

Answer 1

Increases. Negative ions are usually larger than their elements' atoms because more electrons are added, increasing the atomic radius.

Answer 2

The correct answer is (2) increases

The explanation:

when more electrons are added, increasing the atomic radius

with the negative charge means there are more electron than protons, this increases the radius because the positive charge is trying to hold a larger negative charge .