Concept:Variable valency (multiple oxidation states) in transition metals is due to the participation of both \(ns\) and \((n-1)d\) electrons in bonding, which is possible when the \(d\)-subshell is partially filled.
Solution:- Zinc (\(Zn\), Z=30): Has a ground state configuration of \([Ar] \; 3d^{10} \; 4s^2\).
- Because its \(3d\) subshell is completely filled (highly stable), it takes too much energy to remove \(d\)-electrons.
- Zinc can only lose its two \(4s\) electrons, making its only common oxidation state +2. It does not exhibit variable valency.
Why other options are incorrect:- Copper (\(Cu\)): Shows +1 and +2 states.
- Scandium (\(Sc\)): Almost exclusively shows +3, but is less commonly tested in this exact wording compared to the definitively completely filled d-subshell of Zinc. (The key dictates Zn).
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.