Identify an actinoid element from the following.

The reason for lanthanoid contraction is

Which of the following is not a consequence of the Lanthanoid contraction?

Select the incorrect statement about lanthanides.

Describe the atomic and ionic radii of lanthanoids and explain lanthanoid contraction.

Fill in the blanks:
$1.$ The atomic radii of the elements of the third transition series are .......... to those of the corresponding elements of the second transition series.
$2.$ Samarium melts at .......... $K$.
$3.$ The color of lanthanoid ions is due to the presence of .......... electrons.