Which one of the following is smallest in size?

Options

A. B
B. AI
C. In
D. Ga

Answer

To determine which element is the smallest in size among the given options, we will analyze the elements of Group 13 (the boron family): boron (B), aluminum (Al), gallium (Ga), and indium (In).

### Step-by-Step Solution:

1. **Identify the Elements and Their Atomic Numbers**:
- Boron (B) - Atomic Number: 5
- Aluminum (Al) - Atomic Number: 13
- Gallium (Ga) - Atomic Number: 31
- Indium (In) - Atomic Number: 49

2. **Understand the Electronic Configuration**:
- Boron: 1s² 2s² 2p¹
- Aluminum: 1s² 2s² 2p⁶ 3s² 3p¹
- Gallium: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p¹
- Indium: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p¹

3. **Analyze the Trend in Atomic Size**:
- Atomic size generally increases as you move down a group in the periodic table. This is due to the addition of electron shells, which increases the distance between the nucleus and the outermost electrons.
- In this case, as we move from boron to indium, we are adding more electron shells:
- Boron has 2 shells.
- Aluminum has 3 shells.
- Gallium has 4 shells.
- Indium has 5 shells.

4. **Determine the Smallest Element**:
- Since boron is at the top of the group with the least number of electron shells, it will have the smallest atomic size compared to aluminum, gallium, and indium.

5. **Conclusion**:
- Therefore, among the given elements, boron (B) is the smallest in size.

### Final Answer:
The smallest element in size among boron, aluminum, gallium, and indium is **Boron (B)**.

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