What does the group number of a elements in the a/b numbering system)
tell about valence electrons?

a. the a group number tells which period the valence electrons are
in
b. the a group number tells how much mass the elements have.
c. all elements in the same a group will have the same number of
valence electrons.
d. all elements in the a group will have the same valence electrons
as the b group.

All elements in the same A group will have the same number of

valence electrons.

Explanation:

Group A has 1 valence electrons.

oh it is true if thats what you are asking

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer