To determine the number of neutrons in an atom of magnesium-25 (Mg-25), we start with the information given by its name. The ‘-25’ indicates the atomic mass of this isotope, which is the sum of protons and neutrons in the nucleus of the atom.
Magnesium has an atomic number of 12, which means that it has 12 protons. The atomic mass number (A) of Mg-25 is 25. The number of neutrons can be calculated using the formula:
Number of Neutrons = Atomic Mass Number (A) – Atomic Number (Z)
Plugging in the values:
Number of Neutrons = 25 – 12 = 13
Thus, an atom of Mg-25 contains 13 neutrons.