In the field of nano-technology, scientists study particles that are extremely small. These particles are measured in nanometers (nm), which is one billionth of a meter. The correct answer is option 2, which states that the size of particles being studied in nano-technology is about 1-100 nm.

Option 1 states that the size of particles being studied is 1 A - 10 nm. This is incorrect because an angstrom (A) is equal to 0.1 nm, so the range mentioned in option 1 is much smaller than the correct answer.

Option 3 states that the size of particles being studied is 1-50 p. This is incorrect because `p` is not a recognized unit of measurement. Most likely it is a typo, and the intended unit may have been `pm` (picometers), but the range mentioned in the option is still smaller than the correct answer.

Option 4 states that the size of particles being studied is 1 mm - 10 mm. This is incorrect because millimeters (mm) are much larger than nanometers (nm), and the range mentioned in the option is far beyond the size of particles studied in nano-technology.

Overall, the correct range for the size of particles