The figure below shows a cube. Which one of the following faces, P, Q, R or S in the figure is not part of the net of the cube?

1. Mentally fold the net to identify overlapping faces.

Let the blank square directly below P be the Right face, and R be the Base.
Folding the net:

• The blank square below P becomes the Right face.
• P (above the Right face) folds to become the Top face.
• Q is attached to the right of P. When P is the Top face, Q folds down to become the Left face.
• However, S (to the left of R) already folds up to become the Left face.
  Since Q and S would overlap and occupy the same position (the Left face), one of them must be removed. Removing S would disconnect the blank square below it, so Q must be the extra face.