Question

the elements in group 17 of the periodic table are all called halogens. all halogens have the same
atomic number.
atomic mass.
number of possible isotopes.
number of valence electrons.

Explanation:

Halogens are in group 17 of the periodic table. The chemical properties of elements are mainly determined by the number of valence electrons. Elements in the same group have the same number of valence electrons. Halogens have 7 valence electrons. The number of possible isotopes varies among different halogen elements. The atomic mass and atomic number are specific to each element in the group and are not the same for all halogens.

Answer:

number of valence electrons