An electric dipole, made up of positive and negative charges, each of $1 \mu \mathrm{C}$ and placed at a distance $2 \mathrm{~cm}$ apart. If the dipole is placed in an electric field of $10^{5} \mathrm{~N} / \mathrm{C}$ then the maximum torque which the field can exert on the dipole, if it is turned from a position $\theta=0^{c}$ to $\theta=180^{\circ}$ is, is :
(a) $2 \times 10^{-3} \mathrm{~N}-\mathrm{m}$
(b) $3 \times 10^{-3} \mathrm{~N}-\mathrm{m}$
(c) $4 \times 10^{-3} \mathrm{~N}-\mathrm{m}$
(d) $2.8 \times 10^{-3} \mathrm{~N}-\mathrm{m}$