Choose the incorrect statement among the following:
the chemistry of different lanthanoids is very similar
4f⁻ and 5f⁻ orbitals are equally shielded
d-block element show irregular and erratic chemical properties among themselves
La and Lu have partially filled d-orbitals

Option A: True. The shielding of Lanthanoids is very similar.
Option B: False: 4f and 5f belong to different main energy levels, so the shielding effects on them are not the same. Shielding effect of 4f is more than that of 5f.
Option C: True. d⁻block elements are transition elements between metals and non-metals and hence, show irregular chemical properties among themselves.
Option D: Electronic configuration - 57La: [Xe] 6s²5d¹ 71Lu: [Xe] 6s²4f¹⁴5d¹
Both have partially filled d-orbitals.
Hence, B is the only option which is incorrect.