The f-block elements are those in which the differentiating electrons enters the (n-2)f orbitals. There are two series of f-Block elements corresponding to filling of 4f and 5f-orbitals. The series of 4f-orbitals is called lanthanides. Lanthanides show different oxidation states depending upon stability of f⁰, f⁷ and f¹⁴ configurations, though the most common oxidation states is +3. There is a regular decrease in the size of lanthanides ions with increase in atomic number which is known as lanthanides contraction.

Which of the following is the incorrect statement?

The different radii of Zr and Hf due to consequences of the lanthanide contraction.

The correct answer is option 2. The different radii of Zr and Hf due to consequences of the lanthanide contraction.

Let us revisit the statements, especially focusing on the relationship between Zr (zirconium) and Hf (hafnium) with respect to the lanthanide contraction:

1. Lanthanide contraction is the accumulation of successive shrinkages.

This statement is correct. The term "lanthanide contraction" describes the phenomenon where the atomic and ionic radii of the lanthanide series elements decrease as the atomic number increases, due to the poor shielding effect of the 4f electrons.

2. The different radii of Zr and Hf due to consequences of the lanthanide contraction.

This statement is incorrect. The correct concept is that the lanthanide contraction causes Zr and Hf to have similar radii, not different radii. Because of the lanthanide contraction, hafnium, which follows the lanthanides, has a radius very close to that of zirconium, even though hafnium has more protons and electrons.

3. Shielding power of 4f electrons is quite weak.

This statement is correct. The 4f electrons do not shield the nuclear charge effectively, which results in the increasing effective nuclear charge experienced by the outer electrons across the lanthanide series.

4. There is a decrease in the radii of the atoms or ions proceeds from La to Lu.

This statement is correct. The radius of lanthanides generally decreases from lanthanum (La) to lutetium (Lu) due to the increasing nuclear charge and poor shielding effect of the 4f electrons.

So, the correct answer is indeed option 2, as the lanthanide contraction causes Zr and Hf to have similar radii, not different.

Corrected Explanation: The incorrect statement is: The different radii of Zr and Hf due to consequences of the lanthanide contraction.

The correct understanding is that the lanthanide contraction results in Zr and Hf having very similar radii, despite Hf having a higher atomic number. This is due to the poor shielding of the 4f electrons, which causes the effective nuclear charge to be similar for both elements, leading to similar atomic sizes.