The element with a mass number of 230 is thorium (Th). Thorium has an atomic number of 90, which means it has 90 protons in its nucleus. The mass number of an element represents the total number of protons and neutrons in its nucleus. Since thorium has an atomic number of 90, it means it has 90 protons. Therefore, to determine the number of neutrons, we subtract the atomic number from the mass number:
Neutrons = Mass number - Atomic number = 230 - 90 = 140
So, thorium-230 has 90 protons and 140 neutrons in its nucleus.