Moderate# Zero Fields and Potentials

SATPHY-EYLQ5W

The picture below shows four pairs of uniformly charged spheres. The red spheres are positively charged; the blue spheres are negatively charged. Each sphere has the same amount of charge. Assume each pair is isolated.

For which pair is there a point between them on the dotted line where the electric field magnitude is zero and a point between them on the dotted line where the electric potential is zero?