2023 H2 Chem P1 Q1 — Atomic structure Solution

The answer is B.
From the Data Booklet, Nd has proton number 60 and Pm has proton number 61. Both isotopes have 145 nucleons (protons + neutrons).
• \(\text{Nd}^{2+}\): neutrons \(= 145 - 60 = 85\); electrons \(= 60 - 2 = 58\).
• \(\text{Pm}^{3+}\): neutrons \(= 145 - 61 = 84\); electrons \(= 61 - 3 = 58\).
So \(\text{Nd}^{2+}\) has more neutrons (85 against 84) and both ions have the same number of electrons (58), which is row B.
• A is wrong: both ions have 58 electrons, so \(\text{Nd}^{2+}\) does not have more electrons.
• C is wrong: \(\text{Pm}^{3+}\) has fewer neutrons (84), and \(\text{Nd}^{2+}\) does not have more electrons.
• D is wrong: the electron column is right, but \(\text{Pm}^{3+}\) has fewer neutrons than \(\text{Nd}^{2+}\) (84 against 85), because Pm has one more proton in the same 145 nucleons.