Question

Two point charges of the same magnitude and opposite sign are fixed at points A and B. A third point charge is to be balanced at P by the electrostatic force due to these 2 charges. The Point P :
a)lies on the perpendicular bisector of line AB
b) is at the mid point of line AB
c) lies to left of A
d) none

Answer 1

test charge is always positive 
the magnitude of test charge is not given hence, we can place left & right of A on balancing magnitude of charge and distance of charge hence option (D) is correct.