Which of the following is the number of neutrons in the most abundant isotope of argon (argon-40)?

• A. 22
• B. 22
• C. 20
• D. 18

Answer: (A)

Verified step by step guidance

1. Identify the atomic number of argon, which is the number of protons in the nucleus. Argon has an atomic number of 18.
2. Recognize that the isotope notation 'argon-40' indicates the mass number (A), which is the total number of protons and neutrons in the nucleus, is 40.
3. Recall the relationship between mass number (A), number of protons (Z), and number of neutrons (N): \(A = Z + N\).
4. Rearrange the formula to solve for the number of neutrons: \(N = A - Z\).
5. Substitute the known values for argon-40: \(N = 40 - 18\), which gives the number of neutrons in the most abundant isotope of argon.