Explain:

Why do $\mathrm{Zr}$ and $\mathrm{Hf}$ exhibit similar properties?

The outer electronic configuration of two members of the lanthanide series are as follows:

$4{\mathrm{f}}^{1}5{\mathrm{d}}^{1}6{\mathrm{s}}^2$ and $4{\mathrm{f}}^{7}5{\mathrm{d}}^{0}6{\mathrm{s}}^2$.

What are their atomic numbers? Predict the oxidation states exhibited by these elements in their compounds.

Select the correct match:

The $\mathrm{X}, \mathrm{Y}$ and $\mathrm{Z}$, respectively are

Choose the correct statements:

$\left(\mathrm{I}\right)$ The size of the lanthanoid ${\mathrm{M}}^{3+}$ ions decreases as the atomic number of $\mathrm{M}$ increases.
$\left(\mathrm{II}\right)$ Electronic spectra of lanthanoid shows very broad bands.
$\left(\mathrm{III}\right)$ As with transition metals, coordination number six is very common in lanthanoid complexes.