Identify the incorrect statement among the following

We examine every option one by one and check it against the known behaviour of transition-metal and inner-transition-metal orbitals.

Option A: “d-Block elements show irregular and erratic chemical properties among themselves.”
Within the same period, successive d-block elements differ in oxidation state, magnetic behaviour, catalytic activity, etc. This irregularity arises from small differences in $$3d$$, $$4d$$, $$5d$$ subshell energies, the comparable energies of $$ns$$ and $$(n-1)d$$ orbitals, and the lanthanoid contraction. Hence the statement is correct.

Option B: “La and Lu have partially filled d orbitals and no other partially filled orbitals.”
Electronic configurations:
$$La: [Xe]\,6s^2\,5d^1\,4f^0$$
$$Lu: [Xe]\,6s^2\,5d^1\,4f^{14}$$
Both possess a single electron in the $$5d$$ orbital; their $$4f$$ shells are either empty ($$La$$) or completely filled ($$Lu$$). Thus only the d orbital is partially filled. The statement is correct.

Option C: “The chemistry of various lanthanoids is very similar.”
All lanthanoids predominantly show the +3 oxidation state and have comparable ionic radii (lanthanoid contraction). This causes their chemical reactions—complex formation, basicity of hydroxides, etc.—to be almost identical. Hence the statement is correct.

Option D: “$$4f$$ and $$5f$$ orbitals are equally shielded.”
Shielding (screening) depends on the radial extension of orbitals. $$4f$$ orbitals are buried deep inside the atom and are poorly shielded by outer electrons, whereas $$5f$$ orbitals extend further from the nucleus and experience better shielding by $$6s$$, $$6p$$ electrons. Therefore the two sets of orbitals are not shielded to the same extent. This statement is incorrect.

The only incorrect statement is Option D which is: $$4f$$ and $$5f$$ orbitals are equally shielded.