Congruent polygons are polygons that have the same size and the same shape. We can see from the diagram that the figure in pair 2 has been rotated to form the second figure in the pair. Since the shape and size were not changed, they are congruent.
The figure in pair 3 has also been rotated; this again preserves size and shape, so the figures are congruent.
The figure in pair 4 sees to have been reflected. This did not change the size or shape of the figure, so the pair is congruent.
