Which isotope of argon (Ar) has 22 neutrons?

• A. Ar-39
• B. Ar-36
• C. Ar-38
• D. Ar-40

Answer: (C)

Verified step by step guidance

1. Recall that the number of neutrons in an isotope is given by the difference between the mass number (A) and the atomic number (Z): \(\text{Neutrons} = A - Z\).
2. Identify the atomic number of argon (Ar), which is the number of protons. Argon has an atomic number \(Z = 18\).
3. For each isotope, subtract the atomic number from the mass number to find the number of neutrons. For example, for Ar-39, neutrons = \$39 - 18$.
4. Calculate the number of neutrons for each isotope: Ar-36, Ar-38, Ar-39, and Ar-40, using the formula \(\text{Neutrons} = A - 18\).
5. Compare the calculated neutron numbers to 22 and identify which isotope corresponds to 22 neutrons.