Although zirconium belongs to 4d transition series and hafnium to 5d transition series even then they show similar physical and chemical properties because …….. .

Options

A. both belong to d-block
B. both have same number of electrons
C. both have similar atomic radius
D. both belong to the same group of the periodic table.

Explanation

To answer the question of why zirconium (Zr) and hafnium (Hf) exhibit similar physical and chemical properties despite belonging to different transition series (4d and 5d respectively), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Elements**:
- Zirconium (Zr) is part of the 4d transition series.
- Hafnium (Hf) is part of the 5d transition series.

2. **Understand the Concept of Lanthanide Contraction**:
- Lanthanide contraction refers to the phenomenon where the atomic and ionic sizes of the lanthanide series elements decrease with increasing atomic number due to the poor shielding effect of the f-orbitals.

3. **Relate Lanthanide Contraction to Zr and Hf**:
- The poor shielding effect of the f-electrons in the lanthanides leads to a greater effective nuclear charge felt by the outer electrons in the subsequent elements. This results in a smaller atomic radius for elements following the lanthanides.

4. **Compare Atomic Radii**:
- Due to lanthanide contraction, the atomic radius of hafnium (Hf) is very similar to that of zirconium (Zr). This similarity in size is crucial for their chemical behavior.

5. **Conclude the Similar Properties**:
- Because Zr and Hf have similar atomic radii, they also have similar physical and chemical properties. This is primarily due to the fact that similar sizes allow for similar bonding characteristics and interactions with other elements.

### Final Answer:
Zirconium and hafnium show similar physical and chemical properties primarily because of **lanthanide contraction**, which results in their atomic radii being very similar despite being in different transition series.

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