1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(1)3d^51s22s22p63s23p64s13d5
This is an unusual config......and "Hund's rule"Hund's rule of maximum multiplicity operates; half-filled electronic orbitals are somewhat stabilized. In 1st year chem, you probably would not have to know this......in 2nd year inorganic chem., you would have to know this.
Upon ionization, the 4s4s and 3d3d electrons are removed to give Cr^(2+)Cr2+, 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^41s22s22p63s23p63d4; Cr^(3+)Cr3+, 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^31s22s22p63s23p63d3.