C

In a charged capacitor, the energy is stored in the electric field that exists between the plates.
Step 1: Understand that a capacitor consists of two conductive plates separated by an insulating material. When a voltage is applied, one plate accumulates positive charge while the other accumulates negative charge.
Step 2: The electric field is created in the region between the plates due to this separation of charges. This electric field is responsible for storing electrical energy.
Step 3: The energy ( ext{U}) stored in a capacitor can be expressed using the formula:
$$U = \frac{1}{2} C V^2$$
where $C$ is the capacitance and $V$ is the voltage across the capacitor.
Step 4: Examining the options:

• Option A: The positive charges - This is incorrect as energy is not only related to the positive charges.
• Option B: Both the positive and negative charges - While both contribute to the total charge, they do not store energy by themselves.
• Option C: The field between the plates - This is correct as the primary location of energy storage is the electric field between the capacitor plates.
• Option D: Around the edge of the capacitor plates - This is incorrect since the energy does not reside in this area.

Therefore, the correct answer is C.