Concept: Metals form positive ions by losing electrons, which changes their size.
Explanation: A neutral metal atom has its normal atomic radius.
When a metal loses its outermost electrons to form a cation, it often loses an entire electron shell.
With fewer shells and less electron-electron repulsion, the remaining electrons are pulled closer to the nucleus.
This makes the ionic radius smaller than the atomic radius.
For example, a sodium atom
Na is larger than its ion
Na+.
Therefore, ionic radii of metals are usually less than their atomic radii.
Answer: D. less than their atomic radii.