An electric dipole of moment $p$ is placed at $60°$ to a uniform electric field of magnitude $E$. The torque on the dipole is:

**Torque on a dipole.** $\tau = pE \sin\theta$, where $\theta$ is the angle between the dipole moment and the field. **Substitute.** With $\theta = 60°$, $\sin 60° = \dfrac{\sqrt 3}{2}$, so $\tau = \dfrac{\sqrt 3}{2}\,pE$. **Distractor logic.** Option B uses $\cos 60° = 1/2$ instead of $\sin$. Option A is the maximum torque (would need $\theta = 90°$). Sine, not cosine — the torque is zero when the dipole *aligns* with the field, so it must use $\sin\theta$.