The magnetic moment `$\left(\mu \right)$  of a revolving electron around the nucleus varies with principal quantum number n as 

From Bohr’s model of atom, electrons can revolve only in those orbits in which their angular momentum is an integral multiple of $\text{h/2}\pi$ where h is

Planck’s universal constant.

From Bohr’s postulate

$\mu =\frac{\text{nh}}{2\pi }\Rightarrow \mu \propto \text{n}$

Where n is integer $\left(=1,2,3\cdots \right)$ and is called principal quantum number