The locus of the points which is equidistant from the line PQ forms a

The locus of points which are equidistant from the line PQ is a line that is perpendicular to PQ and passes through the midpoint of PQ. This is because a point is equidistant from a line if and only if it is on the perpendicular bisector of the line segment connecting any two points on the line. So, the correct option is "perpendicular line to PQ". The points on this line are equidistant from the line PQ, and the line passes through the midpoint of PQ, which is equidistant from both P and Q. A circle with center P or Q would not include all the points equidistant from PQ, and a pair of parallel lines would not be equidistant from PQ.