Step 1: Understanding the question.
We are given that the energy stored in both the parallel and series combinations of capacitors is the same. The energy stored in a capacitor is given by \( E = \frac{1}{2} C V^2 \). Since the energy is the same, we can equate the energies for both combinations.
Step 2: Analyzing the parallel and series combinations.
- In the parallel combination, the total capacitance is \( C_{parallel} = 3C \).
- In the series combination, the total capacitance is \( C_{series} = \frac{C}{3} \).
Step 3: Deriving the ratio.
The potential difference across each combination must satisfy the energy condition. By equating the energies, we find that the ratio of potential differences \( \frac{V_{parallel}}{V_{series}} = \frac{1}{\sqrt{3}} \). This gives the correct answer as \( \frac{1}{3} \).