Statement I: The actinide contraction is more as compared to the lanthanide contraction.
Statement II: 5f electrons have much lower shielding effect as compared to 4f electrons because 5f orbitals are more diffused than 4f orbitals. 

Options

A. If both Statement I and Statement II are true and Statement II is the correct explanation of Statement I.
B. If both Statement I and Statement II are true but Statement II is not the correct explanation for Statement I.
C. If Statement I is true but Statement II is false.
D. If Statement I is false but Statement II is true.

Answer

To analyze the statements provided in the question, we will evaluate each statement separately and determine their correctness.

### Step 1: Understand Actinide and Lanthanide Contraction

**Actinide Contraction:**
- Actinides are the series of elements from actinium (Ac) to lawrencium (Lr), which involve the filling of 5f orbitals.
- The actinide contraction refers to the gradual decrease in atomic and ionic radii of actinide elements as the atomic number increases.

**Lanthanide Contraction:**
- Lanthanides are the series of elements from lanthanum (La) to lutetium (Lu), which involve the filling of 4f orbitals.
- The lanthanide contraction similarly refers to the decrease in atomic and ionic radii of lanthanide elements as the atomic number increases.

### Step 2: Compare the Magnitude of Contractions

- The actinide contraction is generally more pronounced than the lanthanide contraction. This is due to the fact that the 5f orbitals are more diffused and have a lower shielding effect compared to the 4f orbitals.
- As a result, the effective nuclear charge experienced by the outer electrons in actinides is greater, leading to a more significant contraction.

### Step 3: Evaluate Statement I

**Statement I:** "The actinide contraction is more as compared to the lanthanide contraction."
- This statement is **True**. The actinide contraction is indeed more pronounced than the lanthanide contraction.

### Step 4: Understand Shielding Effect of Electrons

**Shielding Effect:**
- The shielding effect refers to the ability of inner electrons to shield outer electrons from the full effect of the nucleus's positive charge.
- In the case of 4f and 5f orbitals, the 4f electrons have a higher shielding effect compared to the 5f electrons.

### Step 5: Evaluate Statement II

**Statement II:** "5f electrons have much lower shielding effect as compared to 4f electrons because 5f orbitals are more diffused than 4f orbitals."
- This statement is also **True**. The 5f orbitals are indeed more diffused, leading to a lower shielding effect compared to the more compact 4f orbitals.

### Conclusion

Both statements are true:
- **Statement I:** True
- **Statement II:** True

### Final Answer

Both statements are correct.

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