The second and third row elements of transition maetals resemle each other much more than they resemble the first row because of

Options

A. lanthanoid contraction which results in almost same radii of second and third row metals
B. diagonal relationship between second and third row elements
C. similar ionisation elethalphy of second and third row elements
D. similar oxidation states of second and third row metals.

Answer

To solve the question regarding why the second and third row elements of transition metals resemble each other more than they resemble the first row, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Transition Metals**:
- Transition metals are found in the d-block of the periodic table. They are divided into three rows: the first row (3d), the second row (4d), and the third row (5d).

2. **Identify the Key Concept**:
- The key concept here is the **lanthanide contraction**. This refers to the phenomenon where the atomic and ionic sizes of the lanthanide series elements (elements 57 to 71) decrease as we move from lanthanum (La) to lutetium (Lu).

3. **Explain Lanthanide Contraction**:
- The lanthanide contraction occurs because the 4f electrons do not shield the nuclear charge effectively. As a result, the effective nuclear charge felt by the outer electrons increases, pulling them closer to the nucleus and resulting in smaller atomic radii.

4. **Compare the Atomic Radii**:
- Due to the lanthanide contraction, the atomic radii of the second row (4d transition metals) and third row (5d transition metals) transition metals become similar. This similarity in size leads to similar chemical and physical properties.

5. **Conclusion**:
- Therefore, the second and third row transition metals resemble each other much more than they resemble the first row because of the lanthanide contraction, which results in similar atomic radii.

### Final Answer:
The second and third row elements of transition metals resemble each other much more than they resemble the first row because of the **lanthanide contraction**, which leads to similar atomic radii.

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