Which of the following is NOT a type of quadrilateral?

The answer C, Hexagon, is correct because a hexagon is defined as a polygon with six sides. In contrast, all the other options—square, trapezoid, and rectangle—are types of quadrilaterals, which are polygons that have exactly four sides. A square has equal sides and right angles, a rectangle has opposite equal sides and right angles, and a trapezoid features at least one pair of parallel sides. Understanding the classification of polygons is key to distinguishing between the different shapes; therefore, recognizing that a hexagon does not fit the criteria for a quadrilateral is essential.