GKFix MCQ Question

What is the potential at point D due to the charge at B (-q) at diagonal distance d√2?

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