If two atoms have the same number of protons in their nucleus, you can conclude for sure that they:

• A. are atoms of the same element
• B. have the same mass number
• C. are isotopes of each other
• D. have the same number of neutrons

Answer: (A)

Verified step by step guidance

1. Recall that the number of protons in an atom's nucleus is called the atomic number, and it uniquely identifies the element.
2. Understand that atoms with the same number of protons belong to the same element, regardless of differences in neutrons or mass number.
3. Recognize that the mass number is the sum of protons and neutrons, so atoms with the same number of protons can have different mass numbers.
4. Know that isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons.
5. Conclude that if two atoms have the same number of protons, they are definitely atoms of the same element, but they may differ in neutrons and mass number.