Well, first of all, there's no such thing as "fully charged" for a capacitor.
A capacitor has a "maximum working voltage", because of mechanical or chemical reasons, just like a car has a maximum safe speed. But anywhere below that, cars and capacitors do their jobs just fine, without any risk of failing.
So we have a capacitor that has some charge on it, and therefore some voltage across it. From the list of choices above . . .
<span>-- Both plates have the same amount of charge. Yes. And both plates have opposite TYPES of charge. One plate is loaded with electrons and is negatively charged. The other plate is missing electrons and is positively charged.
-- There is a potential difference between the plates. Yes. That's the "voltage" mentioned earlier. It's a measure of how badly the extra electrons want to jump from the negative plate to the positive plate.
-- Electric potential energy is stored. Yes. It's the energy that had to be put into the capacitor to move electrons away from one plate and cram them onto the other plate.
