The atomic number of an element is determined by the number of protons in its nucleus. For nitrogen, the atomic number is 7, as it has 7 protons.
The mass number, on the other hand, is the sum of the number of protons and neutrons in the nucleus. In the case of the radioactive isotope of nitrogen with 9 neutrons, the mass number would be calculated as follows:
Mass number = Number of protons + Number of neutrons
Mass number = 7 protons + 9 neutrons = 16
Therefore, the atomic number of this radioactive nitrogen isotope is 7, and its mass number is 16.