Which of the following pairs has almost same radii ?

Options

A. `Al, Ga`
B. `Be,Mg`
C. `Mg,Cl`
D. `B,Be`

Explanation

To determine which of the following pairs has almost the same radii, we will analyze the atomic structures and properties of the elements in the provided pairs.

### Step-by-Step Solution:

1. **Identify the Elements in the Pair**:
- We need to consider the elements mentioned in the question. Let's take the first pair as an example: Aluminium (Al) and Gallium (Ga).

2. **Write the Electronic Configuration**:
- Aluminium (Al): The electronic configuration is \( [Ne] 3s^2 3p^1 \).
- Gallium (Ga): The electronic configuration is \( [Ar] 4s^2 3d^{10} 4p^1 \).

3. **Analyze the Presence of d Electrons**:
- Gallium has 10 electrons in the 3d subshell. The presence of these d electrons affects the atomic radius due to their poor shielding effect.

4. **Understand the Shielding Effect**:
- The d electrons in Gallium do not effectively shield the nucleus from the outer electrons. This results in a stronger effective nuclear charge felt by the outer electrons, which pulls them closer to the nucleus.

5. **Compare the Atomic Radii**:
- Due to the poor shielding effect of the d electrons in Gallium, the atomic radius of Gallium is smaller than what would be expected if it followed the trend of its group. However, it is still comparable to Aluminium's radius.

6. **Conclusion**:
- Therefore, Aluminium and Gallium have almost the same atomic radii due to the combined effects of their electronic configurations and the shielding effect of the d electrons in Gallium.

### Final Answer:
The pair that has almost the same radii is Aluminium (Al) and Gallium (Ga).

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