In which of the following pairs do the elements have nearly the same densities ?

In which of the following pairs, both species have not nearly the same size ?

Because of lanthnoid contractoin, which of the following pairs of elements have nearly same atomic radii ? (Number in the parentrhesis are atomic numbers)

Because of lanthnoid contraction, which of the following pairs of elements have nearly same atomic radii ? (Number in the parenthesis are atomic numbers)

Which of the following series of elements have nearly the same atomic radii