Conjugacy Class of Element of Center is Singleton

Theorem
Let $G$ be a group.

Let $\map Z G$ denote the center of $G$.

The elements of $\map Z G$ form singleton conjugacy classes, and the elements of $G \setminus \map Z G$ belong to multi-element conjugacy classes.

Proof
Let $\conjclass a$ be the conjugacy class of $a$ in $G$.