What does the superscript in the notation 40/19 K represent?

In the notation 40/19 K, the superscript (40) represents the mass number of the potassium isotope. The mass number is the total count of protons and neutrons in an atom's nucleus. In this particular case, the atomic symbol K corresponds to potassium, which has an atomic number of 19, indicating that it has 19 protons. The mass number of 40 means that the potassium isotope has a total of 40 nucleons (which are protons and neutrons combined).

To determine the number of neutrons in this potassium isotope, one can subtract the atomic number from the mass number. Therefore, this specific potassium isotope (40/19 K) has 21 neutrons (40 - 19 = 21). Understanding that the superscript shows the mass number is crucial for interpreting various isotopes and their properties in atomic theory.