Which of the following best describes how an isotope differs from the standard form of a chemical element?

• A. An isotope has a different chemical symbol than the standard element.
• B. An isotope has a different number of protons but the same number of neutrons as the standard element.
• C. An isotope has a different number of electrons but the same number of protons as the standard element.
• D. An isotope has a different number of neutrons but the same number of protons as the standard element.

Answer: (D)

Verified step by step guidance

1. Recall that the chemical symbol of an element is determined by the number of protons in its nucleus, which defines the element itself.
2. Understand that isotopes are variants of the same element, meaning they have the same number of protons but differ in the number of neutrons.
3. Recognize that changing the number of protons would change the element entirely, so isotopes cannot differ in proton number.
4. Note that electrons can vary in ions, but isotopes specifically refer to differences in the nucleus, not the electron count.
5. Therefore, the key difference for isotopes is a different number of neutrons while maintaining the same number of protons as the standard element.