Final answer:
Two atoms can have the same atomic mass if they have the same number of protons and neutrons, making them isotopes with equal mass numbers. Isotopes are variants of the same element with different numbers of neutrons but the same number of protons and electrons. Option c, 'They have the same number of neutrons,' is the correct explanation for why two atoms could have the same atomic mass.
Step-by-step explanation:
To address the question of how two atoms can have the same atomic mass, it is crucial to understand the concept of isotopes. An atom is the smallest unit of an element that retains the properties of that element, consisting of a nucleus surrounded by electrons. The atomic mass of an atom is primarily determined by the number of protons and neutrons in its nucleus, as they have a mass of 1 atomic mass unit each. Isotopes are atoms of the same element which have the same number of protons but different numbers of neutrons, resulting in different atomic masses.
Two atoms can have the same atomic mass if they have the same number of protons and neutrons. The atomic number (Z), which is the number of protons in the nucleus, defines the element's identity, and for a neutral atom, this number is also equal to the number of electrons. However, the neutron number (N) can vary among atoms of the same element, leading to different isotopes with the same atomic mass if their total number of protons and neutrons is the same.
Therefore, to answer your question, two atoms can have the same atomic mass if they have the same number of neutrons (option c). This means they could be isotopes of different elements with equal mass numbers, or identical isotopes of the same element. The number of isotopes does not affect the atomic mass directly, so option d is not relevant in this context. It is the combination of protons and neutrons that equals the mass number, hence determining the atomic mass.