Deuterium is an isotope of hydrogen with a mass number of 2. Which of the following correctly describes a deuterium atom?

• A. It has 2 protons, 2 neutrons, and 2 electrons.
• B. It has 1 proton, 2 neutrons, and 1 electron.
• C. It has 2 protons, 0 neutrons, and 1 electron.
• D. It has 1 proton, 1 neutron, and 1 electron.

Answer: (D)

Verified step by step guidance

1. Recall that the atomic number of hydrogen is 1, which means every hydrogen atom has exactly 1 proton.
2. Understand that the mass number of an isotope is the sum of protons and neutrons in the nucleus.
3. Since deuterium has a mass number of 2 and 1 proton, calculate the number of neutrons by subtracting protons from the mass number: \(\text{neutrons} = 2 - 1\).
4. Recognize that a neutral atom has the same number of electrons as protons, so deuterium has 1 electron.
5. Combine these facts to describe deuterium as having 1 proton, 1 neutron, and 1 electron.