Question

how is the atomicity of fluorine 6?

Answer 1

Atomic number of F is 9 and the valence electrons are 7. It requires one electron to attain noble gas configuration and combines with one more F atom to form F₂ molecule.
Atomicity is the number of atoms present in one molecule of that element. Fluorine has 2 atoms in its molecule. So atomicity of F is 2 and not 6.​