Which isotope of argon has 22 neutrons?

• A. Ar-40
• B. Ar-38
• C. Ar-42
• D. Ar-36

Answer: (A)

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): \(\text{Number of neutrons} = A - Z\).
2. Identify the atomic number (Z) of argon, which is the number of protons. Argon has an atomic number of 18.
3. For each isotope option, subtract the atomic number (18) from the mass number (the number after 'Ar-') to find the number of neutrons.
4. Calculate the neutrons for each isotope: For example, for Ar-40, neutrons = \$40 - 18\(; for Ar-38, neutrons = \)38 - 18$, and so on.
5. Compare the calculated number of neutrons for each isotope to 22, and select the isotope where the number of neutrons equals 22.