Question

9
which of the following statements is true of the mass number of an atom?
a. the mass number of an atom is equal to the sum of its number of protons and neutrons.
b. the mass number of any atom can be found on the periodic table.
c. the mass number of an atom always has the same value as its average atomic mass.
d. all of these
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Explanation:

The mass number is defined as the sum of protons and neutrons in an atom's nucleus. The periodic table lists average atomic mass (a weighted average of isotopes), not mass number. Mass number differs from average atomic mass because isotopes have varying neutron counts. Thus, only option A is correct.

Answer:

A. The mass number of an atom is equal to the sum of its number of protons and neutrons.