Lanthanoid contraction will not have any influence when we compare size of :-

Options

A. Zr & Hf
B. Y & La
C. Mo & W
D. Tc & Re

Answer

**Step-by-Step Solution:**

1. **Understanding Lanthanoid Contraction:**
- Lanthanoid contraction refers to the gradual decrease in the size of lanthanide ions as we move from lanthanum (La) to lutetium (Lu) in the periodic table. This occurs because the f-orbitals are being filled, and the shielding effect of these f-electrons is relatively poor.

2. **Identifying the Elements:**
- The lanthanide series consists of elements from atomic number 57 (Lanthanum, La) to 71 (Lutetium, Lu). The elements that follow the lanthanides in the periodic table include transition metals.

3. **Analyzing the Influence of Lanthanoid Contraction:**
- The contraction affects the size of the elements that follow the lanthanides. For example, yttrium (Y) and zirconium (Zr) are influenced by the lanthanoid contraction due to their positions in the periodic table.

4. **Finding the Exception:**
- The question asks for an element whose size is not influenced by lanthanoid contraction. Yttrium (Y) is an element that is often considered to be less affected by this contraction because it is not directly following the lanthanides in the periodic table.

5. **Conclusion:**
- Therefore, when comparing sizes, the lanthanoid contraction will not have any influence when we compare the size of yttrium (Y) with other elements that follow the lanthanides.

**Final Answer:**
- The size of yttrium (Y) will not be influenced by lanthanoid contraction.

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