An electric dipole is placed at the centre of a sphere. Mark the correct answer

Inside the sphere, net charge is zero due to dipole.

${\mathrm{q}}_{\mathrm{in}}=0 \Rightarrow {\mathrm{\varphi }}_{\mathrm{sphere}}=\frac{{\mathrm{q}}_{\mathrm{in}}}{{\mathrm{\epsilon }}_0}=0$

Potential due to the dipole will be zero at the plane perpendicular to the dipole and passing through the mid-point of the dipole. This equi-potential surface of the dipole intersect the sphere and form a circle on the sphere. This circular intersection will have zero potential.

Hence, electric potential is zero on a circle on the surface.