Final answer:
The direction of the force on a negative charge in an electric dipole setup is towards the positive charge. The options provided suggest that if +ŷ is towards the positive charge, then the force on -q will be in the +ŷ direction.
Step-by-step explanation:
The direction of the force on a negative charge (-q) in an electric field can be determined by considering the properties of electric fields and charges. Electric fields originate from positive charges and terminate at negative charges. Since like charges repel and opposite charges attract, a negative charge will be repelled by another negative charge and attracted to a positive charge.
For an electric dipole, which consists of a positive charge (+2q) and a negative charge (-2q), the electric field lines emanate outwards from the positive charge and terminate at the negative charge. If we place a negative charge (-q) equidistant from both charges in a dipole, the field lines will show that this charge is attracted to the positive charge and repelled by the negative charge. Therefore, overall force on -q will be oriented towards the positive charge, as this attractive force outweighs the repulsive force due to the negative dipole charge.
From the given options, the force on –q would be directed towards the positive charge of the dipole, not up, down, left, or right, and certainly not zero as there is a net force acting on it. Given the provided context with -ŷ and +ŷ directions, if +ŷ is towards the positive charge and -ŷ is towards the negative charge, then the correct answer would be +ŷ direction.