What method of notation expresses the identity of an atom by listing the atomic number and mass number?

The method of notation that expresses the identity of an atom by listing the atomic number and mass number is known as isotopic notation. This notation typically takes the format where the mass number is placed at the top left of the element symbol and the atomic number is placed at the bottom left. For example, carbon-12 would be represented as ( \text{^{12}_{6}C} ), where 12 is the mass number (total number of protons and neutrons) and 6 is the atomic number (number of protons).

Using isotopic notation is particularly useful in distinguishing between different isotopes of an element, which have the same number of protons but different numbers of neutrons, leading to different mass numbers. This notation helps in various fields, including chemistry and nuclear physics, where understanding isotopes can be crucial for reactions, stability, and applications such as radiometric dating or medical imaging.

Other options include nuclear notation, which is similar but typically more focused on nuclear properties than the standard citation of atomic and mass numbers; molecular notation, which describes compound molecules rather than individual atoms; and elemental notation, which generally refers to the element symbol alone without specific reference to isotopic identity. Hence, isotopic notation is the most