What characteristic shared between chlorine, fluorine, and bromine makes them have similar properties?

a. all have two electrons in their first energy levels.
b. all have the same number of protons in their outermost energy levels.
c. all have a similar state of matter.
d. all have seven valence electrons.

The correct answer is option(D)

Explanation:

All chlorine , fluorine,and bromine are members of group 17 also known as halogens.

The general electronic configuration of group 17 is written as:

,

Here 'n' is the valence shell or outer most shell present in the atom of an element.

They have fully filled s-orbital and incomplete p-orbital by one electron. There are seven valence electrons present in their valence shell. Hence the correct answer from the given options is option (D).