Question

Which of the following pairs has the same size?

• A. $Fe^{2+},Ni^{2+}$
• B. $Zr^{4+},Ti^{4+} $
• C. $Zr^{4+},Hf^{4+} $
• D. $Zn^{2+},Hf^{4+} $

Answer 1

The Correct Option is C

In general, the atomic and ionic radii increases on moving down a group but the elements of second transition series $(Zr, Nb, Mo)$ have almost same radii as the elements of third transition series $(Hf, Ta, W, etc)$. This is because of lanthanoid contraction, i.e.
imperfect shielding of one $4f\, e^- $ by another.