The given statement is,
If a polygon is a quadrilateral, then it has four right angles.
To write a counterexample to the given statement:
The statement, "If a polygon is a quadrilateral, then it has four right angles" is not always possible.
Because rhombus is one such figure which has four sides and none of its angles are right angles.
Thus, a counterexample for the statement, "If a polygon is a quadrilateral, then it has four right angles" is Rhombus.