A polygon has 20 sides. Find the maximum number of acute angles that the polygon can have. ?

The sum of the exterior angles of a polygon is 360. So, there can't be more than 3 exterior angles which are greater than 90. Hence, there can't be more than 3 interior angles which are acute.

Interior Angle + Exterior angle in a convex polygon = 180

any polygon irrespective of sides have a maximum of three acute angles

But it is not written that the polygon is convex. In the case of convex, it will be 3.