Which of the following is the atomic number of helium?

• A. 4
• B. 2
• C. 10
• D. 1

Answer: (B)

Verified step by step guidance

1. Recall that the atomic number of an element is the number of protons in the nucleus of an atom of that element.
2. Identify helium on the periodic table, where it is located in Group 18 and Period 1.
3. Note that helium has 2 protons in its nucleus, which defines its atomic number.
4. Understand that the atomic mass (approximately 4 for helium) is different from the atomic number.
5. Therefore, the atomic number of helium is 2, not 4, 10, or 1.