To solve this problem, we need to understand the concept of lanthanoid contraction.$\newline$Lanthanoid contraction refers to the gradual decrease in the atomic and ionic radii of the lanthanide series elements from $La$ (57) to $Lu$ (71).$\newline$This contraction occurs due to the poor shielding effect of the 4f electrons.$\newline$As a result, the elements following the lanthanides in the periodic table, such as $Hf$ (72), have atomic radii similar to those of the elements preceding the lanthanides, such as $Zr$ (40).$\newline$Let's analyze the options:$\newline$• Option 1: Zr (40) and Nb (41) - These elements are consecutive in the periodic table, but Nb is not significantly affected by lanthanoid contraction.$\newline$• Option 2: Zr (40) and Hf (72) - Due to lanthanoid contraction, Hf has a similar atomic radius to Zr. This is the correct pair.$\newline$• Option 3: Zr (40) and Ta (73) - Although Ta follows Hf, its atomic radius is not as similar to Zr as Hf's is.$\newline$• Option 4: Ti (22) and Zr (40) - These elements are in the same group, but Ti is not affected by lanthanoid contraction.$\newline$Therefore, the correct option is Option 2, where Zr and Hf have nearly the same atomic radii due to lanthanoid contraction.