Lanthanoids have greater tendency to form complexes than actinoids.
Actinoid contraction is greater than lanthanoid contraction.
Hydroxides of actinoids are less basic than Lathanoid hydroxides.
Binding energy of $4 \mathrm{f}$ - orbitals is lower that $5 \mathrm{f}$ - orbitals.
Solution
To determine the correct answer, let's analyze the options:
1. "Lanthanoids have greater tendency to form complexes than actinoids."
- This is false because actinoids have a greater tendency to form complexes due to their higher charge density and variable oxidation states compared to lanthanoids.
2. "Actinoid contraction is greater than lanthanoid contraction."
- This is true because the 5 f orbitals in actinoids are less shielded than the $4 f$ orbitals in lanthanoids. This causes a stronger actinoid contraction compared to lanthanoid contraction.
3. "Hydroxides of actinoids are less basic than lanthanoid hydroxides."
- This is false because lanthanoid hydroxides are less basic than actinoid hydroxides due to lanthanoids having lower ionic radii and less shielding effect.
4. "Binding energy of $4 f$ orbitals is lower than $5 f$ orbitals."
- This is false because $5 f$ orbitals in actinoids are less tightly bound than $4 f$ orbitals in lanthanoids.
So Option 2 is Correct