Answer: K, F (Potassium, Fluorine)
Explanation: Ionic bonds are formed by transfer of electrons between metal and non metals.
Covalent bonds are formed by sharing of electrons between non metals.
Electronic configuration of potassium:
[tex][K]:19:1s^22s^22p^63s^23p^64s^1[/tex]
Potassium atom will lose one electron to gain noble gas configuration and form [tex]K^+[/tex].
[tex][K^{+}]:18:1s^22s^22p^63s^23p^6[/tex]
Electronic configuration of fluorine:
[tex][F]:9:1s^22s^22p^5[/tex]
Fluorine atom will gain one electron to gain noble gas configuration and form [tex]F^-[/tex].
[tex][F^-]:10:1s^22s^22p^6[/tex]
In potassium fluoride the one electron from potassium metal gets transferred to fluorine atom and thus form an ionic bond to give [tex]KF[/tex]
