A line parallel to the line ab
A line perpendicular to the line ab through the mid-point of ab
A circle through a and b with centre at the mid-point of ab
A circle with centre at a and passes through b
A circle in a plane perpendicular to ab and centre at the mid-point of the line ab
Correct answer is B
The locus of all points having a distance of 1 unit from each of the two fixed points. a and b is: a perpendicular to the (ab) through the mid-points ab