The correct answer is B. Fermi.
A fermi is a unit of length equal to 10â15 meters. It is named after Enrico Fermi, an Italian-American physicist who was awarded the 1938 Nobel Prize in Physics for his contributions to the development of nuclear fission.
The radius of a nucleus is typically on the order of 10â15 meters, or 1 fermi. Therefore, the fermi is the most suitable unit for expressing nuclear radius.
The other options are not as suitable for expressing nuclear radius. A nanometer is equal to 10â9 meters, which is much larger than the radius of a nucleus. An angstrom is equal to 10â10 meters, which is closer to the radius of a nucleus, but it is not as commonly used as the fermi. A micron is equal to 10â6 meters, which is much larger than the radius of a nucleus.