# Chapter 8 - Problems: 8.40

See explanation below.

#### Work Step by Step

a.) ​[Ar] 4s2 3d10 4p4 is Se (Selenium). The other elements in this group are: O, S, Te, Po, Lv b.) [Xe] 6s2 4f14 5d2 is Hf (Hafnium). The other elements in this group are: Ti, Zr, Rf c.) [Ar] 4s2 3d5 is Mn (Manganese). The other elements in this group are: Tc, Re, Bh

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