The torque $\vec{\tau}$ experienced by an electric dipole is given by the cross product $\vec{\tau} = \vec{p} \times \vec{E}$, with magnitude $\tau = pE \sin\theta$. Here, the electric field $\vec{E}$ is along the positive z-direction, and the dipole moment $\vec{p}$ is along the negative z-direction. The angle $\theta$ between them is $180^\circ$. Since $\sin(180^\circ) = 0$, the torque is zero. Note: The non-uniformity of the field ($dE/dz$) results in a net force on the dipole ($F = p \frac{dE}{dz}$), but the torque remains zero because the forces on the charges act along the same line. (See NCERT Physics Class 12, Exercise 1.27).