Answer:
Potassium, barium, copper
Explanation:
Atomic number of potassium = 19
Electronic configuration of potassium =
By loosing one electrons, it attains noble gas configuration.
Atomic number of sulphur = 16
Electronic configuration of sulphur = 
In order to attain noble gas configuration, it has to looses 6 electrons which is not favorable. So, sulphur gains electrons instead of loosing.
Atomic number of fluorine = 9
Electronic configuration of fluorine = 
Fluorine easily attains inert gas configuration by gaining 1 electron.
Atomic number of barium = 56
Electronic configuration of barium = ![[Xe]6s^2](https://tex.z-dn.net/?f=%5BXe%5D6s%5E2)
Barium attains its noble gas configuration by loosing two electrons.
Atomic number of copper = 29
Electronic configuration of copper = ![[Ar]3d^{10}4s^1](https://tex.z-dn.net/?f=%5BAr%5D3d%5E%7B10%7D4s%5E1)
Copper looses one electrons and attains stability. this is because elements having fully filled or half filled sub shell are stable.
So, among given, potassium, barium and copper are expected to lose electrons during chemical changes.