Which of the following atoms has the smallest number of neutrons?

• A. Carbon-12
• B. Oxygen-16
• C. Helium-4
• D. Hydrogen-1 (protium)

Answer: (D)

Verified step by step guidance

1. Identify the number of neutrons in an atom by subtracting the atomic number (number of protons) from the mass number (total number of protons and neutrons). The formula is: \(\text{Number of neutrons} = \text{Mass number} - \text{Atomic number}\).
2. For Carbon-12, the mass number is 12 and the atomic number is 6, so calculate the neutrons as \$12 - 6$.
3. For Oxygen-16, the mass number is 16 and the atomic number is 8, so calculate the neutrons as \$16 - 8$.
4. For Helium-4, the mass number is 4 and the atomic number is 2, so calculate the neutrons as \$4 - 2$.
5. Compare the number of neutrons calculated for each atom to determine which has the smallest number of neutrons. Note that Hydrogen-1 (protium) has a mass number of 1 and an atomic number of 1, so it has \$1 - 1 = 0$ neutrons, which is the smallest possible.