Answer 1

Following are the similarities between actinoids and lanthanoids:-

(i) Size of atom: It decreases across the series in both actinoids (due to actinoid contraction) and lanthanoids (due to lantanoid contraction).

(ii) Oxidation states: Lanthanoids and actinoids generally show +3 oxidation states. However, some elements in the actinoid series are capable of exhibiting oxidation states higher than +3.

Disclaimer: Any one of the above mentioned similarity is sufficient.