Concept:The number of unpaired electrons dictates properties like melting point, binding energy, and paramagnetism. Electrons fill the \(d\)-orbitals singly until they are forced to pair up.
Solution:- Moving from left to right across the d-block:
- Group III B (Sc) has 1 unpaired electron (\(d^1\)).
- Group IV B (Ti) has 2 unpaired electrons (\(d^2\)).
- Group V B (V) has 3 unpaired electrons (\(d^3\)).
- Group VI B (Cr) achieves a maximum of 6 unpaired electrons (\(3d^5 \; 4s^1\)).
- After Group VI B, electrons begin to pair (e.g., Fe in VIII has 4, Cu in I B has 1). Therefore, the number of unpaired electrons increases progressively up to V B and VI B.
Why other options are incorrect:- Groups I B and II B are at the far right of the block where almost all electrons are paired.
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