Which device operates based on electrostatic principles and is used for printing?

A laser printer operates on electrostatic principles, making it the correct answer. This type of printer uses a laser beam to create an electrostatic image of the page to be printed on a photosensitive drum. The drum is charged in various areas where the laser hits it, creating a latent image. Toner, which is a fine powder, is then attracted to the charged areas to form the image, which is subsequently transferred to paper and fused using heat.

The other devices listed work on different principles. An inkjet printer utilizes liquid ink that is sprayed onto paper, which relies on fluid dynamics rather than electrostatics. A 3D printer creates three-dimensional objects by building up layers of material, often using techniques like extrusion or resin curing, and does not function through electrostatic means. A thermal printer operates by using heat to transfer ink from a ribbon onto paper or to change the color of heat-sensitive paper, which again is not based on electrostatics. Therefore, the unique principle utilized by laser printers distinguishes them in the context of the question.