Assertion : `4d` and `5d` series elements have nearly same atomic radius.
Reason : Lanthanoid contraction.

Options

A. Statement-1 is true , Statement-2 is true and Statement-2 is correct explanation for Statement-1
B. Statement-1 is true, Statement-2 is True and Statement-2 is Not correct explanation for statement-1
C. Statement-1 is true, Statement-2 is False
D. Statement-1 is False, Statement-2 is True

Answer

A

Explanation

The atomic radii of the second `(4d series) `and third `(5d series)` transition series are almost the same. This phenomenon is associated with the intervention of the `4f` orbitals which must be filled before the `5d` series of elements begin. The filling of `4f` before `5d` orbital results in a regular decrease in atomic radii called `Lanthanoid contration which essentially compensate for the expected increase in atomic size with increasing atomic number. (The net result of the lanthanoid contraction is that the second and the third d series exhibit similar radii(e.g., Zr 160 pm,Hf 159 pm.)