Concept:These three ions are
isoelectronic, meaning they possess the exact same number of electrons and electron shell configuration. The only thing separating them is the unchanging contents of their respective nuclei.
Formula:$$ \text{Electrons in ion} = Z - \text{Charge} $$
Solution:- Let's analyze their electron counts:
- \( \text{Na}^+ \): \( 11 \text{ (protons)} - 1 \text{ (lost electron)} = 10 \text{ electrons} \).
- \( \text{Mg}^{+2} \): \( 12 \text{ (protons)} - 2 \text{ (lost electrons)} = 10 \text{ electrons} \).
- \( \text{Al}^{+3} \): \( 13 \text{ (protons)} - 3 \text{ (lost electrons)} = 10 \text{ electrons} \).
- Because they all have 10 electrons, their electronic configurations and number of shells (2 shells: K=2, L=8) are perfectly identical.
- However, their atomic numbers (Z) are 11, 12, and 13 respectively. Atomic number dictates the Number of Protons, which remains entirely different and untouched by the ionization process.
Why other options are incorrect:- Options A, B, and C: As proven above, these parameters are identical (10 electrons, \( 1s^2 2s^2 2p^6 \), 2 shells) for all three species.
Quality & Fidelity Assurance:
Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.