Which one among the following is the most appropriate statement with respect to the atomic weight of an element?

The atomic weight of an element is defined as the weighted average of the masses of all its naturally occurring isotopes [1]. While the mass number is always a whole number representing the sum of protons and neutrons in a specific nucleus, the atomic weight is often a fraction or decimal because it accounts for the relative abundance of different isotopes [1]. For example, chlorine has two main isotopes with mass numbers 35 and 37; its atomic weight is approximately 35.5 amu due to their natural distribution [1]. Unlike the mass number, which is specific to a single isotope, the atomic weight represents the element as a whole in nature [1]. Therefore, the most appropriate statement is that the atomic weight can be a fraction, whereas the mass number is strictly an integer [1].

Sources

1. [1] https://www.khanacademy.org/science/biology/history-of-life-on-earth/radiometric-dating/a/atomic-number-atomic-mass-and-isotopes-article