Answer:
B
Explanation:
An element is defined by the number of protons in the nucleus. If you change the number of protons in the nucleus, you change the element you're working with. If you change the number of neutrons, you change the isotope of the element without changing the element itself.
Iron has 26 protons. There are several possible isotopes of iron, but all have 26 protons; it's the number of neutrons that vary. Of the answer options provided, only B gives 26 protons, so only it can be another atom of iron.
