The statement that best summarizes the rotations that turn a square onto itself is: "A square will rotate onto itself after 90-degree, 180-degree, 270-degree, and 360-degree rotations."
This includes all the possible rotations that map the square to its original position: 90 degrees clockwise or counterclockwise, 180 degrees, 270 degrees (which is 90 degrees counterclockwise), and a full 360-degree rotation (which brings it back to its original position).