Which of the following best explains what makes a hydrogen atom different from a helium atom?

• A. A hydrogen atom has one proton, while a helium atom has two protons.
• B. A hydrogen atom has two neutrons, while a helium atom has no neutrons.
• C. A hydrogen atom has more electrons than a helium atom.
• D. A hydrogen atom is heavier than a helium atom.

Answer: (A)

Verified step by step guidance

1. Understand that atoms are defined by their number of protons, which is called the atomic number. This number determines the element's identity.
2. Recall that a hydrogen atom has 1 proton in its nucleus, while a helium atom has 2 protons in its nucleus.
3. Recognize that neutrons and electrons can vary in number, but the defining difference between hydrogen and helium is the number of protons.
4. Note that hydrogen typically has no neutrons (in its most common isotope), and helium usually has 2 neutrons, so the statement about neutrons is incorrect.
5. Conclude that the best explanation for the difference between hydrogen and helium atoms is the difference in the number of protons: hydrogen has one proton, helium has two.