Q. Lanthanide contraction occurs because
A) $f$-orbitals are incompletely filled
B) $f$-orbital electrons are easily lost
C) $f$-orbital do not come out on the surface of atom and are buried inside
D) $f$-orbital electron are poor shielders of nuclear charge
Explanation
(d)
The size of lanthanides are smaller than expected. This is associated with the filling with the filling up of $4f$ orbitals which must be filled before the $5d$ orbitals. The electrons in $f$-orbitals are not effective in screening other electrons from the nuclear charge
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.