How do the atoms of different elements differ from one another?

• A. They have different numbers of neutrons in their nuclei.
• B. They have different numbers of protons in their nuclei.
• C. They have different numbers of electrons in their outermost shell only.
• D. They have different atomic masses but the same number of protons.

Answer: (B)

Verified step by step guidance

1. Understand that atoms of different elements are distinguished by their atomic number, which is the number of protons in the nucleus.
2. Recall that the number of protons defines the element itself, meaning each element has a unique number of protons.
3. Note that while neutrons and electrons can vary (isotopes differ in neutrons, ions differ in electrons), these variations do not change the element identity.
4. Recognize that the number of electrons in the outermost shell affects chemical behavior but does not define the element.
5. Conclude that the fundamental difference between atoms of different elements is the number of protons in their nuclei.