Which of the following objects has the largest $radius$?

• A. A human hair
• B. A proton
• C. The Earth
• D. A basketball

Answer: (C)

Verified step by step guidance

1. Understand that the radius is the distance from the center of an object to its outer edge or surface.
2. Consider the typical sizes of each object: a proton is subatomic and extremely small, on the order of 10^{-15} meters.
3. A human hair has a radius roughly around 10^{-5} meters, which is much larger than a proton but still very small.
4. A basketball has a radius of about 0.1 meters, significantly larger than a human hair.
5. The Earth has a radius of approximately 6.4 \times 10^{6} meters, which is vastly larger than all the other objects listed.