Answer: BF3
Explanation: boron needs 4 electron to obtain octet and Fluorine has just one. For the valence shell to be completely filled it will have to form BF4- with 4 fluorine atom surrounding it.
I assume you mean diato
mic elements.
Those are hydrogen, oxygen, nitrogen, fluorine, chlorine, bromine, and iodine. They all exist in the form

(

). Where they are all bonded to another one of themselves (a hydrogen atom binds to another hydrogen atom, a fluorine atom binds to another fluorine atom, etc.)