Answer:
chlorine
Step-by-step explanation:
In the periodic table , elements are placed together in the same group , because of their same chemical and physical properties .
Fluorine is placed in group 17 ,
Oxygen is placed in group 16 .
And ,
Chlorine is placed in group 17.
Therefore , The chemical properties of fluorine resembles the most with Chlorine , rather than oxygen ,
Because as shown above , the Fluorine and Chlorine are placed in common group number 17.