An increase in the density is seen when moving from Ti to Cu in transition mental series. This can be attributed to ....

Ineffective shielding of d electrons

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):

1. Atomic mass increases continuously because the atomic number increases.

2. The size of the atom does not increase significantly because the d electrons shield the nuclear charge poorly.

3. 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

• Lanthanoid contraction – relevant mainly for 4d and 5d series, not Ti–Cu (3d series).

• Filling of f orbitals prior to d orbitals – incorrect; 3d orbitals are filling here.

• Increase in atomic number and atomic size – atomic size does not increase across the period.

 Ineffective shielding of d electrons is the correct answer.