Which of the following statement is correct ?

Options

A. Because of lanthanide contraction, the separation of second-row d-block elements form one another is easier
B. Because of lanthanide contraction, the radii of the third-row d-block elements are almost the same as those of the second-row elements
C. Because of lanthanide contraction, the radii of the third-row elements are almost the same as those of the first-row elements.
D. The second-row elements have smaller radii than the corresponding third-row elements.

Answer

B

Explanation

The group trends in atomic radii of the d-block elements are parallel to those observed in s- and p- block elements. As we go down the group, there is an increas in atomic size up to the second series of d-block elements. This is expected as the electrons enter the new shell of electrons in the second d-block series. But the atomic radii of the third (5d) series are virtually the same as those of the corresponding members of the second (4d) series. This phenomenon is associated with the intervention of the 4f orbitals. The filling 4f before 5d subshell results in a regular decrease in atomic radii called lanthaboid which essentally compensates for the expected increase in atomic size with increase atomic number. The net result of the lanthanoid contraction is that the second and the third d series exihibit similar radii (e.g., Zr 160 pm, Hf 159 pm) and have very similar physical andchemical properties.