Which of the following pairs have approximately the same atomic radii?

Options

A. Zr and Hf
B. Al and Mg
C. Al and Ga
D. Na and Ne

Answer

To determine which of the following pairs have approximately the same atomic radii, we can analyze the pairs based on their positions in the periodic table and the effects of atomic structure on atomic size.

### Step-by-Step Solution:

1. **Identify the Pairs**:
We need to look at the pairs provided in the question. For this explanation, let's assume the pairs are:
- A) Zirconium (Zr) and Hafnium (Hf)
- B) Aluminium (Al) and Magnesium (Mg)
- C) Aluminium (Al) and Gallium (Ga)
- D) Sodium (Na) and Neon (Ne)

2. **Understand Atomic Radii Trends**:
- Atomic radius generally decreases across a period from left to right due to increasing nuclear charge, which pulls electrons closer to the nucleus.
- Atomic radius generally increases down a group due to the addition of electron shells.

3. **Analyze Each Pair**:
- **Zirconium (Zr) and Hafnium (Hf)**: Both elements are in the same group (Group 4) and show similar atomic radii due to the lanthanoid contraction, which reduces the size of the elements in the f-block. Therefore, they have approximately the same atomic radii.
- **Aluminium (Al) and Magnesium (Mg)**: These elements belong to different groups (Group 13 and Group 2, respectively). Their atomic radii are different due to their positions in the periodic table.
- **Aluminium (Al) and Gallium (Ga)**: Although both are in Group 13, Gallium has a smaller atomic radius than Aluminium due to the presence of d-electrons, which have a poor shielding effect. Thus, they do not have approximately the same atomic radii.
- **Sodium (Na) and Neon (Ne)**: Sodium is a metal in Group 1, while Neon is a noble gas in Group 18. There is a significant difference in their atomic sizes due to their positions in the periodic table.

4. **Conclusion**:
The only pair that has approximately the same atomic radii is **Zirconium (Zr) and Hafnium (Hf)**.

### Final Answer:
**Zirconium (Zr) and Hafnium (Hf) have approximately the same atomic radii.**

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