The statement 'As a result of lanthanoid contraction, the properties of 4d series of the transition elements have no similarities with the 5d series of elements' is incorrect. In fact, due to lanthanoid contraction, the atomic radii of the elements of the second (4d) and third (5d) transition series are virtually the same (e.g., $\text{Zr} = 160 \text{ pm}$ and $\text{Hf} = 159 \text{ pm}$). Because of this similarity in size, they exhibit very similar physical and chemical properties and often occur together in nature, making their separation difficult.