GKFix MCQ Question

What is the potential at the center E due to a single charge +q at corner A?

• A. \frac{+q}{4\pi\epsilon_0 d}
• B. \frac{+q}{4\pi\epsilon_0 (d/\sqrt{2})}
• C. \frac{-q}{4\pi\epsilon_0 d}
• D. Zero