The correct option is A Ca+
Finding the number of valence electrons.
(a) Ca+
Z(Ca) = 20
The electronic configuration of
Ca: 1s22s22p63s23p64s2 or [Ar]4s2
Ca+: 1s22s22p63s23p64s1 or [Ar]4s1
Valence shell electronic configuration of Ca+ : 4s1
Hence, Ca+ does not have 8 electrons in its valence shell.
(b) Rb+
Z(Rb) = 37
The electronic configuration of
Rb: [Ar]3d104s24p65s1
Rb+: [Ar]3d104s24p6
Valence shell electronic configuration of Rb+ : 4s24p6
Hence, Rb+ has 8 electrons in its valence shell.
(c) Xe
Z(Xe) = 54
The electronic configuration of
Xe: [Kr]4d105s25p6
So valence shell electronic configuration of Xe : 5s25p6
Hence, Xe has 8 electrons in its valence shell.
(d) Br−
Z(Br)= 35
The electronic configuration of
Br: [Ar]3d104s24p5
Br−: [Ar]3d104s24p6
So, valence shell electronic configuration of Br− : 4s24p6
Hence, Br− has 8 electrons in its valence shell.