Answer
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