The correct answer is 5.
The order of rotational symmetry is the number of times you can rotate a shape so that it looks the same. The order of rotational symmetry of a regular polygon is the same as the number of sides of the polygon.
If a regular pentagon is rotated by 72° (1/5th of 360°), then it exactly fits its own outline.
Therefore, a regular pentagon has rotational symmetry of order 5.