Answer
The number of valence electrons is:
Ba : 2
Cs : 1
Ni : 10
S : 6
Work Step by Step
The number of valence electrons is determined by the group number of the element.
Ba : 2 (Group 2)
Cs : 1 (Group 1)
Ni : 10 (Group 10)
S : 6 (Group 16 : valence electrons = 16 -10 = 6)