Question

Give reason: Chemistry of actinoids is much more complicated than that of the lanthanides.

Answer 1

Actinoids or actinides are $15$ consecutive chemical elements in the periodic table from actinium to lawrencium. As a group, they are significantly large because of their radioactivity. Although several members of these groups are man-made elements like uranium, they occur naturally. The lanthanide or lanthanoid series of chemical elements comprises the 15 metallic chemical elements with atomic numbers $57 - 71$ from lanthanum through the lutetium.

Complete step-by-step answer: Now about the question, we first need to know what they are as individuals to gain knowledge about the differences and which is more complicated and which is not. Now as we clearly know that the chemistry of actinides is complicated compared to the chemistry of lanthanides. So on this, we mainly have a few reasons for this.
Actinides are radioactive due to that, the chemistry of actinides is complicated, $5 - f$ orbital present in the actinides is more exposed to the outer environment while $4 - f$ orbital present in lanthanides are deeply buried, actinides are mainly present in small quantities, their half-life is extremely small
lanthanides show a limited number of oxidation states as $+ 2, + 3, + 4$, this mainly due to the large energy gap between $4f$ and $5d$ subshells. The dominant oxidation state of actinides is also $+ 3$ but they show a number of other oxidation states.
Transition metals ions from coordination complexes because they have empty valence shell orbitals that can accept pairs of electrons from Lewis base. Ligands must therefore be Lewis bases.
$2Mn{O_4}^ - + 6{H^ + } + 5{O_3}^{2 - } \to 2M{n^{ + 2}} + 5S{O_4}^{2 - } + 3{H_2}O$
Hence this is pretty much the reason why the chemistry of actinides is more complicated than the chemistry of lanthanides.

Note: Thing to remember about actinide and lanthanide is that they both have unfilled orbital of f subshell, lanthanoids to show some similarity with the group 2 elements, and actinides are radioactive elements.