Given:
The quadrilateral PQRS in the diagram is a parallelogram.
Let P'Q'R'S' be the image of PQRS after applying a dilation centered at a point O with scale factor 3.
So, each sides of a parallelogram P'Q'R'S' has enlarged with the scale factor 3.
Hence,
P'Q' = 3PQ
Therefore, the correct option is option B.