Final answer:
On the scale where the Sun is the size of a grapefruit, Earth would correspond to the size of the tip of a ballpoint pen and be located approximately 5 meters away, as per the various scale models suggesting the relative size and distance on a dramatically reduced scale.
Step-by-step explanation:
If the Sun were reduced to the size of a grapefruit, on the same scale, Earth would be option A. The size of the tip of a ballpoint pen, about 5 m away from the Sun. This comparison is derived from several scale models provided, each offering a different perspective but focusing on the drastic size differences between celestial bodies.
In one model, where the Sun is about 100 mm in diameter, the Earth would be about 1 mm in diameter and roughly 12 meters away, suggesting that the Earth is a mere speck in comparison to the Sun. Similarly, in another model where the scale factor is 1 billion, the Earth's diameter is 1.3 centimeters, approximately the size of a grape, with the Sun as a reference for size at 1.5 meters in diameter—at this scale, however, the distance is not preserved, hinting that the other models with detailed distances offer a closer representation.
Given that the question asks for a comparison in both size and distance, we focus on the model where an appropriately scaled Earth would be significantly smaller relative to the proposed grapefruit-sized Sun and positioned at a distance that conveys the vast emptiness of space. Thus, A. The size of the tip of a ballpoint pen, about 5 m away from the Sun, serves as the most accurate answer from the choices provided.