Which statement is true about all uranium atoms?

• A. All uranium atoms have a mass number of 238.
• B. All uranium atoms have the same number of neutrons.
• C. All uranium atoms are radioactive isotopes.
• D. All uranium atoms have 92 protons in their nucleus.

Answer: (D)

Verified step by step guidance

1. Recall that the defining characteristic of an element is its atomic number, which is the number of protons in the nucleus. For uranium, this atomic number is 92, meaning every uranium atom has 92 protons.
2. Understand that the mass number of an atom (sum of protons and neutrons) can vary because atoms of the same element can have different numbers of neutrons, forming isotopes. Therefore, not all uranium atoms have the same mass number or the same number of neutrons.
3. Recognize that uranium has several isotopes, some of which are radioactive and some that are more stable, so it is not true that all uranium atoms are radioactive isotopes.
4. Conclude that the only statement that is always true for all uranium atoms is that they have 92 protons in their nucleus, which defines the element uranium.
5. Summarize that the atomic number (number of protons) is constant for all atoms of an element, while the mass number and neutron count can vary due to isotopes.