GKFix MCQ Question

What is the potential at center E due to charge -q at corner B?

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