An atom of iridium has an atomic number of 77. There are 116 neutrons in the nucleus of a specific atom of iridium. What is the mass number of this atom of iridium

193 This question requires you to know the difference between the atomic number of an element and the atomic mass of an element. Atomic number - number of protons in an element. All atoms of a specific element always have the same number of protons. Atomic mass - the total number of neutrons plus protons in an atom. This number may vary between different atoms in an element. We've been told that the atomic number is 77, which means that there's 77 protons. We've also been told that we have 116 neutrons. So the mass will be: 77 + 116 = 193