Which of the following isotopes has the same number of neutrons as Ca-42?

• A. Ar-40
• B. Sc-43
• C. Ti-44
• D. K-41

Answer: (D)

Verified step by step guidance

1. Identify the number of neutrons in the given isotope Ca-42. The number of neutrons is calculated by subtracting the atomic number (number of protons) from the mass number. For calcium (Ca), the atomic number is 20, so the number of neutrons is \$42 - 20$.
2. Calculate the number of neutrons for each isotope option by subtracting their atomic number from their mass number. For example, for Ar-40, find the atomic number of argon (Ar) and compute \$40 - \text{atomic number of Ar}$.
3. Repeat the neutron calculation for Sc-43 and Ti-44 using their respective atomic numbers and mass numbers.
4. Compare the number of neutrons found in each isotope option to the number of neutrons in Ca-42 to see which one matches.
5. Confirm that the isotope K-41 has the same number of neutrons as Ca-42 by calculating \$41 - \text{atomic number of K}$ and verifying it equals the neutron count of Ca-42.