MHT CET202615 April 2026Morning ShiftChemistryd and f Block ElementsActual
Which of the following factors may be regarded as the main cause of lanthanide contraction?
Options
- APoor shielding of one of 4f electron by another in the sub-shell.
- BEffective shielding of one of 4f electrons by another in the subshell
- CPoorer shielding of 5d electrons by 4f electrons
- DGreater shielding of 5d electrons by 4f electrons
Correct answer
A. Poor shielding of one of 4f electron by another in the sub-shell.
Step-by-step solution
Lanthanide contraction refers to the steady decrease in the atomic and ionic radii of lanthanides with an increase in atomic number. As we move along the lanthanide series, the nuclear charge increases by one unit at each step, and the new electron enters the 4f subshell. The shape of the 4f orbitals is highly diffused, which results in a very poor shielding effect. Consequently, the shielding of one 4f electron by another in the same subshell is inadequate to counterbalance the increased nuclear charge. Due to thi