Assertion: Actinoids form relatively less stable complexes as compared to lanthanoids.

Reason: Actinoids can utilise their 5f orbitals along with 6d orbitals in bonding but lanthanoids do not use their 4f orbital for bonding.

1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is not true but (R) is true.
4. Both (A) and (R) are false.


Hint: Actinides have more tendency to form complex compounds 
Actinides have a somewhat higher tendency to form complex compounds in comparison to lanthanides. This is due to their higher
charge and smaller size of their ions. Actinoids can utilise their 5f orbitals along with 6d orbitals in bonding but lanthanoids do not
use their 4f orbitals for bonding. 
Hence, the Assertion is not true but the reason is true.