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 understand why zirconium (Zr) and hafnium (Hf) exhibit similar physical and chemical properties despite being in different transition series, we can analyze the factors contributing to their similarities step by step.

### Step-by-Step Solution:

1. **Identify the Elements**:
- Zirconium (Zr) is a 4d transition metal.
- Hafnium (Hf) is a 5d transition metal.

2. **Understand the Concept of Transition Metals**:
- Transition metals are elements that have partially filled d orbitals. They are known for their ability to form various oxidation states and complex ions.

3. **Group Position**:
- Both zirconium and hafnium are located in the same group (Group 4) of the periodic table. Elements in the same group often exhibit similar chemical properties due to their similar valence electron configurations.

4. **Atomic Radius**:
- Despite being in different periods, Zr and Hf have similar atomic radii. This is primarily due to the phenomenon known as **lanthanide contraction**.

5. **Lanthanide Contraction**:
- Lanthanide contraction refers to the gradual decrease in the size of the lanthanide series elements as one moves from lanthanum (La) to lutetium (Lu). This contraction affects the elements that follow in the periodic table, particularly the 5d elements like hafnium.
- As a result, hafnium's atomic radius is similar to that of zirconium, despite being in a higher period.

6. **Conclusion**:
- The similarity in atomic radii due to lanthanide contraction leads to similar physical and chemical properties for zirconium and hafnium. Their comparable sizes allow them to form similar types of compounds and exhibit similar reactivity.

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

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