Use Hund’s rule to derive the electronic configuration of `Ce^(3+)` ion, and calculate its magnetic moment on the basis of ‘spin-only’ formula.

Explanation

`Ce(Z=58)=4f^(1)5d^(1)6s^(2),Ce^(3+)=4f^(1)`
There is only one unpaired electgron, i.e., `n=1`, Hence,
`mu=sqrt(n(n+2))=sqrt((1(1+2))=sqrt(3)=1.73BM`