Which of the following is the mass number of a typical helium atom?

• A. 4
• B. 8
• C. 2
• D. 6

Answer: (A)

Verified step by step guidance

1. Understand that the mass number of an atom is the total number of protons and neutrons in its nucleus.
2. Recall that a typical helium atom has 2 protons (which defines it as helium) and usually 2 neutrons.
3. Add the number of protons and neutrons together: mass number = number of protons + number of neutrons.
4. Calculate the mass number for helium: 2 protons + 2 neutrons = 4.
5. Recognize that the mass number 4 corresponds to the typical helium atom, so the correct answer is 4.