= Solution
For the neutral aluminium cluster,
$$
\boxed{N_e=50(3)-12=138.}
$$
This closes the listed sequence through 1I and supports the \b[jellium description of a large metalloid cluster]. Cp\* ligands are counted as monovalent electron-withdrawing surface groups; counting each as a five-electron donor to the entire delocalized core would mix a transition-metal local electron-counting convention with the present shell model. Electron closure is a useful stability criterion, not by itself proof of a perfectly spherical nuclear geometry.
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