What is lanthanoid contraction? Mention the cause for it.

The lanthanoid contraction refers to :

What is lanthanoid contraction? Write the general oxidation state of actinoids.

Give reason: (a) What is lanthanoid contraction? (b) Which is the general oxidation state shown by actinoids?

WHat is lanthanide contraction? Write any one consequence of lanthanid contraction.

What us lanthod contraction ? Write the general oxidation state of actinoids.