Answer: C. Electrons in an ion = protons − charge. \({}^{56}_{26}\text{Fe}^{3+}\) has \(26 - 3 = 23\) electrons. We need the ion with the same electron count.
A: \({}^{59}_{27}\text{Co}^{3+}\) → \(27 - 3 = 24\) electrons. ✗
B: \({}^{52}_{24}\text{Cr}^{2+}\) → \(24 - 2 = 22\) electrons. ✗
C: \({}^{55}_{25}\text{Mn}^{2+}\) → \(25 - 2 = 23\) electrons. ✓
D: \({}^{55}_{25}\text{Mn}^{3+}\) → \(25 - 3 = 22\) electrons. ✗
Only \(\text{Mn}^{2+}\) (option C) matches \(\text{Fe}^{3+}\) at 23 electrons. Note that the mass number (top-left superscript) is irrelevant here — it counts protons + neutrons, not electrons.
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