1. Write the electron configurations of the following elements by using spdf notation: (a) yttrium,.

1. Write the electron configurations of the following elements by using spdf notation: (a) yttrium, (b) hafnium, (c) samarium, (d) rhenium. 2. Write the electron configuration of the following ions using the spdf notation: (a) Cr2+, Cr3+, Cr6+; (b) *Mo3+, Mo4+, Mo6+; (c) Se4+, Se6+, Se2_.