which has poor shielding effect 4f or 5f ?
5f orbital has poor shielding effect than 4f orbital.
This is because 5f orbitals are larger in size as compared to the 4f orbitals. They are more diffused in shape and therefore they can not shield nuclear charge effectively. Due to this actinide shows more contraction in the size than lanthanide because of the presence of 5f orbital in the actinides.