Explain lanthanoid contraction in detail. What is lanthanoid contraction? What are its consequences?

(N/A) $1$. Definition: The steady decrease in the atomic and ionic radii of lanthanoids with an increase in atomic number is known as lanthanoid contraction.
$2$. Cause: It is due to the imperfect shielding of one $4f$ electron by another in the same subshell. As the nuclear charge increases by $1$ unit at each step,the $4f$ electrons fail to shield the outer electrons effectively from the increased nuclear attraction,leading to a contraction in size.
$3$. Consequences:
$(a)$ Similarity in properties: Elements of the second and third transition series (e.g.,$Zr$ and $Hf$) have almost identical atomic radii due to lanthanoid contraction.
$(b)$ Difficulty in separation: Due to the similarity in ionic radii and chemical properties,it is very difficult to separate lanthanoids from their mixtures.
$(c)$ Basic strength: The basic strength of lanthanoid hydroxides decreases from $La(OH)_3$ to $Lu(OH)_3$ as the size decreases and covalent character increases.