To determine the number of neutrons in a single [tex]\( Fe^{2+} \)[/tex] ion, we need to first understand the relationship between the mass number, the atomic number, and the number of neutrons.
The mass number (denoted as [tex]\( A \)[/tex]) is the total number of protons and neutrons in the nucleus of an atom.
The atomic number (denoted as [tex]\( Z \)[/tex]) is the number of protons in the nucleus of an atom. For the element iron (Fe), the atomic number is 26. This means that any iron atom (or ion) has 26 protons.
The number of neutrons (denoted as [tex]\( N \)[/tex]) can be calculated using the formula:
[tex]\[
N = A - Z
\][/tex]
Given:
- The mass number [tex]\( A = 56 \)[/tex]
- The atomic number [tex]\( Z = 26 \)[/tex]
Substituting these values into the formula:
[tex]\[
N = 56 - 26 = 30
\][/tex]
Therefore, a single [tex]\( Fe^{2+} \)[/tex] ion has 30 neutrons.
Hence, the correct answer is:
30.
