Final answer:
The normal viewing distance for a TV monitor is not explicitly answered in the question, but it should exceed the near point of the eye, which is around 25 cm for a person with normal vision. None of the provided options are suitable ergonomic viewing distances for a 15-20 inch TV monitor.
Step-by-step explanation:
The question regarding the normal viewing distance for a 15-20 inch TV monitor relates to the concept of visual acuity and the near point of the eye. For clear vision, the image distance (di) must be equivalent to the lens-to-retina distance, which is a constant within the eye. With a normal vision range from 25 cm (near point) to infinity (far point), this is indicative of the minimum distance at which one should view a monitor.
While the question does not provide a definitive answer, as viewing distances can vary based on individual comfort and health recommendations, the option closest to advised ergonomic guidelines, considering the near point, is option 2. Thus, a typical recommended viewing distance for a 15-20 inch TV monitor would be greater than the near point of the eye, so none of the given distances are ideal. However, as a guideline, more comfortable viewing distances for monitors are often suggested to be at least an arm's length away.