The correct answer is b. The molecule F2 is made up of two fluorine atoms. Fluorine has an atomic number of 9, which means that it has 9 protons and 9 electrons. The first two electrons fill the first energy shell, the next six electrons fill the second energy shell, and the last electron is the valence electron. Since fluorine has only one valence electron, it needs to share this electron with another atom to complete its outer shell.
In the Lewis dot structure for F2, each fluorine atom shares its valence electron with the other fluorine atom. This forms a single bond between the two fluorine atoms. The resulting molecule is F2, which is also known as fluorine gas.
The other answer choices are incorrect:
A. F-F: This Lewis dot structure shows two fluorine atoms with double bonds between them. However, fluorine atoms can only form single bonds.
C. F:::F: This Lewis dot structure shows two fluorine atoms with triple bonds between them. However, fluorine atoms can only form single bonds.
D. F...F: This Lewis dot structure shows two fluorine atoms with no bonds between them. However, fluorine atoms need to form bonds with other atoms to complete their outer shells.
Therefore the correct option is b.