Which isotope of argon has 22 neutrons?

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

Answer: (D)

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 18. This means every argon atom has 18 protons.
3. For each isotope, subtract the atomic number (18) from the mass number (A) to find the number of neutrons. For example, for Ar-36, neutrons = \$36 - 18$.
4. Calculate the number of neutrons for each isotope: Ar-36, Ar-39, Ar-40, and Ar-38 (even if not listed as an option) to see which has 22 neutrons.
5. Compare the calculated neutron numbers to 22 and identify the isotope whose neutron count matches 22.