Which statement must be true about a polygon?

Here are five statements about polygons, with one incorrect:

1. Correct: A polygon is a closed shape with straight sides.
2. Correct: The sum of the interior angles of a triangle is always 180°.
3. Correct: A regular polygon has all sides and angles equal.
4. Correct: The sum of the interior angles of a quadrilateral is always 360°.
5. Incorrect: The sum of the interior angles of a pentagon is 500°.

Explanation: The sum of the interior angles of a pentagon is actually 540° (calculated as (n-2) × 180°, where n = 5). All the other statements about polygons are correct