An atom of chlorine and an atom of bromine have the same:

• A. group number in the periodic table
• B. number of protons
• C. atomic mass
• D. number of electrons in a neutral atom

Answer: (A)

Verified step by step guidance

1. Recall that elements in the same group (vertical column) of the periodic table have similar chemical properties because they have the same number of valence electrons.
2. Understand that the group number corresponds to the number of valence electrons in the outer shell for main-group elements, which influences chemical behavior.
3. Recognize that chlorine (Cl) and bromine (Br) are both halogens, located in Group 17 of the periodic table, so they share the same group number.
4. Note that chlorine and bromine have different numbers of protons (atomic numbers) and different atomic masses because they are different elements.
5. Also, in their neutral atomic states, chlorine and bromine have different numbers of electrons equal to their respective protons, so the number of electrons is not the same.