When does the torque acting on an electric dipole in a uniform electric field become zero?

An electric dipole in a uniform electric field experiences (when it is placed at an angle $\theta$ with the field):

$A$ point particle of charge $Q$ is located at $P$ along the axis of an electric dipole $1$ at a distance $r$ as shown in the figure. The point $P$ is also on the equatorial plane of a second electric dipole $2$ at a distance $r$. The dipoles are made of opposite charges $q$ separated by a distance $2a$. For the charged particle at $P$ not to experience any net force,which of the following correctly describes the situation?

An electric dipole of length $2 \ cm$ is placed with its axis making an angle of $60^{\circ}$ to a uniform electric field of $10^{5} \ N/C$. If it experiences a torque of $8 \sqrt{3} \ Nm$,calculate the magnitude of the charge on the dipole. (Given: $\sin 60^{\circ} = \frac{\sqrt{3}}{2}$)

The electric dipole is situated in an electric field as shown in figure $(i)$. The dipole and electric field are both in the plane of the paper. The dipole is rotated about an axis perpendicular to the paper at point $A$ in an anticlockwise direction. If the angle of rotation is measured with respect to the direction of the electric field,then the torque for different values of the angle of rotation $\theta$ will be as represented in Fig. $(ii)$.

An electric dipole is placed in an electric field generated by a point charge. Which of the following statements is correct?