If the protons and electrons are the only basic charges in the universe, all the observable charges have to be integral multiples of $e$. Thus, if an object contains $x$ electrons and $y$ protons, the net charge on the object will be

$(y-x) e$

The correct answer is Option (4) → $(y-x) e$

Given:

Charge on one electron $= -e$

Charge on one proton $= +e$

If an object contains $x$ electrons and $y$ protons,

Then total charge,

$q = (+y e) + (-x e) = (y - x)e$

∴ Net charge on the object is $q = (y - x)e$