Zr and Zn have the same oxidation state +2. Size of lanthanoid decrease because of poor screening of

Options

A. 4f
B. 3d
C. 5f
D. 4d

Answer

To solve the question regarding the size of lanthanides and the comparison of zirconium (Zr) and zinc (Zn) with the same oxidation state of +2, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding Oxidation States**:
- Both zirconium (Zr) and zinc (Zn) can exhibit a +2 oxidation state. This means they both lose two electrons to achieve this state.

2. **Comparing Zr and Zn**:
- Zr is a d-block element (transition metal) while Zn is also a d-block element but is a post-transition metal. The electronic configurations are:
- Zr: [Kr] 5s² 4d²
- Zn: [Ar] 4s² 3d¹⁰
- Despite having the same oxidation state, their sizes differ due to their positions in the periodic table and the nature of their electron configurations.

3. **Understanding Lanthanide Contraction**:
- The size of lanthanides decreases as we move from La to Lu. This phenomenon is known as lanthanide contraction.
- The contraction occurs due to the poor shielding effect of the 4f electrons.

4. **Shielding Effect**:
- In lanthanides, as electrons are added to the 4f subshell, these electrons do not effectively shield the nuclear charge from the outer electrons (6s and 6p).
- This poor shielding leads to a stronger effective nuclear charge felt by the outer electrons, resulting in a decrease in size.

5. **Conclusion**:
- The size of lanthanides decreases because of the poor screening of the 4f electrons, which leads to a stronger attraction between the nucleus and the outer electrons, causing the atomic radius to shrink.

### Final Answer:
The size of lanthanides decreases due to the poor screening effect of the 4f electrons.

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