An increase in the density is seen when moving from Ti to Cu in transition mental series. This can be attributed to ....
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Ineffective shielding of d electrons
An increase in density is seen when moving from Ti to Cu in the transition metal series due to ineffective shielding of d electrons.
Across the transition series (Ti → Cu):
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Atomic mass increases continuously because the atomic number increases.
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The size of the atom does not increase significantly because the d electrons shield the nuclear charge poorly.
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Due to this ineffective shielding, the increasing nuclear charge pulls electrons closer, so atomic volume remains almost constant or decreases slightly.
Since
Density = Mass / Volume
Mass increases while volume changes very little, so density increases across the series.
OTHER OPTIONS
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Lanthanoid contraction – relevant mainly for 4d and 5d series, not Ti–Cu (3d series).
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Filling of f orbitals prior to d orbitals – incorrect; 3d orbitals are filling here.
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Increase in atomic number and atomic size – atomic size does not increase across the period.
Ineffective shielding of d electrons is the correct answer.