What is lanthanoid contraction? What are the consequences of lanthanoid contraction?

(N/A) As we move along the lanthanoid series,the atomic number increases gradually by $1$. This means that the number of electrons and protons present in an atom also increases by $1$. As electrons are being added to the same shell,the effective nuclear charge increases. This happens because the increase in nuclear attraction due to the addition of a proton is more pronounced than the increase in the interelectronic repulsions due to the addition of an electron. Also,with the increase in atomic number,the number of electrons in the $4f$ orbital also increases. The $4f$ electrons have poor shielding effect. Therefore,the effective nuclear charge experienced by the outer electrons increases. Consequently,the attraction of the nucleus for the outermost electrons increases. This results in a steady decrease in the size of lanthanoids with the increase in the atomic number. This is termed as lanthanoid contraction.
Consequences of lanthanoid contraction:
$i$. There is similarity in the properties of the second and third transition series.
$ii$. Separation of lanthanoids is possible due to lanthanoid contraction.
$iii$. It is due to lanthanoid contraction that there is a variation in the basic strength of lanthanoid hydroxides. (Basic strength decreases from $La(OH)_3$ to $Lu(OH)_3$).