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:

1. Atomic number: Each element has a unique atomic number, so halogens (different elements like F, Cl, Br, etc.) have different atomic numbers. Eliminate this option.
2. Atomic mass: Atomic mass varies among halogens (e.g., F has a different atomic mass than Cl). Eliminate this option.
3. Number of possible isotopes: Different halogens have different numbers of isotopes (e.g., Cl has 2 stable isotopes, F has 1 stable isotope). Eliminate this option.
4. Number of valence electrons: Elements in the same group have the same number of valence electrons. Group 17 elements (halogens) have 7 valence electrons. This is correct.

Answer:

number of valence electrons.