Four charges, $q_a,q_b,q_a,$ and $q_d$ are fixed at the corners of a square. A charge $q$ that is free to move located at the exact center of the square.

Classify the scenarios described according to the force that would be exerted on the center charge $q.$ Assume in each case that $q$ is a positive charge. Do not assume that the fixed charges have equal magnitudes unless the scenario defines such an equality.