Final answer:
The mass number isn't listed on the periodic table because it can vary for different isotopes. Instead, the atomic mass is provided, which is an average reflecting the masses of all naturally occurring isotopes of that element. Scientists communicate specific isotopes using nuclear symbols or naming conventions.Hence, the correct answer is option B.
Step-by-step explanation:
The mass number is not listed with each element on the periodic table primarily because mass number can vary for isotopes of a given element. Elements can have many isotopes, which are atoms with the same number of protons but different numbers of neutrons. There are over 3,500 isotopes known for all the elements, and isotopes affect properties such as nuclear stability. Instead, the periodic table provides the atomic mass, which is an average that reflects the mass numbers of all naturally occurring isotopes.
Scientists usually represent the mass number of an atom by writing a nuclear symbol or by giving the name of the element with the mass number written, enabling the differentiation of various isotopes. For example, carbon (C) has isotopes like carbon-13 and carbon-14, distinguished by their mass numbers: 13 and 14, respectively.
The periodic table does show each element's atomic mass and atomic number. The atomic number, which is the number of protons, appears above the element's symbol, while the atomic mass, approximating the average mass of the isotopes, is usually placed below the element's symbol.