The magnitude of torque ($\tau$) exerted on an electric dipole in a uniform electric field ($E$) is given by the formula: $\tau = pE \sin\theta$ where $p$ is the dipole moment, defined as the product of the magnitude of one of the charges ($q$) and the distance separating them ($2a$). $p = q(2a)$ Substituting this into the torque equation: $\tau = q(2a)E \sin\theta$

Given: $\tau = 4$ N m $E = 2 \times 10^5$ N/C $\theta = 30^\circ$ (so $\sin 30^\circ = 0.5$) Dipole length ($2a$) = 2 cm = $2 \times 10^{-2}$ m

Substituting these values to solve for charge $q$: $4 = q \times (2 \times 10^{-2}) \times (2 \times 10^5) \times 0.5$ $4 = q \times (2 \times 10^3)$ $q = \frac{4}{2 \times 10^3} = 2 \times 10^{-3}$ C $q = 2$ mC