Compare the chemistry of actinoids with that of the lanthanoids with special reference to :
Atomic and ionic sizes

Explanation

Atomic and ionic sizes : Both lanthanoids and actinoids show decrease in size of their atoms and `M^(3+)` ions with increasing atomic number. Decrease in atomic radii (often called lanthanoid contraction and actinoid contraction, respectively) is not regular. However, decrease in ionic radii (for `M^(3+)` ion) is more regular. The contraction is greater in actinoids resulting from poor shielding by 5f - electrons than that by 4f - electrons in lanthanoids.