An atom would become a different element if which of the following characteristics changed?

• A. The number of neutrons in its nucleus
• B. The number of electrons in its outer shell
• C. Its atomic mass
• D. The number of protons in its nucleus

Answer: (D)

Verified step by step guidance

1. Understand that an element is defined by its atomic number, which is the number of protons in the nucleus of an atom.
2. Recognize that changing the number of neutrons changes the isotope of the element but does not change the element itself.
3. Know that changing the number of electrons affects the ionization state or charge of the atom but does not change the element.
4. Realize that atomic mass is the sum of protons and neutrons, so changing it alone does not necessarily change the element.
5. Conclude that only changing the number of protons in the nucleus changes the atomic number and thus transforms the atom into a different element.