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Answer:
regular octagon
Explanation:
In order for a shape to tessellate a plane, there must be a way to arrange the shapes so that the sum of angles at a node is 360°. An arrangement of kites is shown in the attachment. Of course, squares are used to tile planes all the time, as their four 90° corners fit together nicely.
An octagon has internal angles of 135°, which is not a sub-multiple of 360°. Hence there is no way for octagons to fit together to tile a plane.
Octagons will not tessellate a plane.