c
Electric dipole moment, \(p =4 \times 10^{-9} \,C\, m\)

Angle made by \(p\) with a uniform electric field, \(\theta=30^{\circ}\) Electric field,

\(E =5 \times 10^{4} \,N \,C ^{-1}\)

Torque acting on the dipole is given by the relation,

\(\tau= pE \sin \theta\) \(=4 \times 10^{-9} \times 5 \times 10^{4} \times \sin 30\)

\(=20 \times 10^{-5} \times \frac{1}{2}=10^{-4} \,N\,m\)

Therefore, the magnitude of the torque acting on the dipole is \(10^{-4} \;N \,m\)