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

Explanation

Cerium has the configuration :
`[Xe]4f^(1)5d^(1)6s^(2)`
Configuration of `Ce^(3+)` may be written as :
`[Xe]4f^(1)`, i.e., there is only one unpaired electron, i.e., n = 1.
Hence, magnetic moment is given by :
`mu=sqrt(n(n+2))=sqrt(1(1+2))=sqrt(3)=1.73` BM.