Step 1: Frame the comparison. The question asks how the 4f (lanthanoid) and 5f (actinoid) families behave for two properties. The key physical reason for every difference is that 5f orbitals are more spread out and shield the nucleus less than 4f orbitals.
Step 2: Sizes. Moving left to right in each series, radii shrink because each new f-electron adds little shielding while nuclear charge keeps increasing, so the net (effective) nuclear pull grows. This is the lanthanoid contraction in the 4f series and the actinoid contraction in the 5f series. The actinoid contraction is a shade larger per step because 5f electrons shield even less well.
Step 3: Oxidation states. For lanthanoids the +3 state is overwhelmingly the most stable, with occasional +2 and +4 exceptions. For actinoids many oxidation states appear (+3, +4, +5, +6, even +7) because the 5f, 6d and 7s levels are so close in energy that a variable number of electrons can be used in bonding.
Step 4: One-line contrast. Lanthanoids = smaller contraction, mostly +3; actinoids = slightly larger contraction, many variable oxidation states. This variability also makes actinoid chemistry richer and, together with their radioactivity, more complex than that of the lanthanoids.