Which isotope of iron has 30 neutrons?

• A. Fe-56
• B. Fe-58
• C. Fe-54
• D. Fe-57

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 iron (Fe), which is 26. This means every iron atom has 26 protons.
3. For each isotope option, subtract the atomic number (26) from the mass number (the number after Fe) to find the number of neutrons.
4. Calculate the neutrons for Fe-54: \$54 - 26 = 28\( neutrons; for Fe-56: \)56 - 26 = 30\( neutrons; for Fe-57: \)57 - 26 = 31\( neutrons; for Fe-58: \)58 - 26 = 32$ neutrons.
5. Compare the calculated neutron numbers to the target number (30 neutrons) and identify the isotope that matches, which is Fe-56.