The correct order of atomic radii in group 13 elements is

Options

A. `B lt Ga lt Al gt Ti lt In`
B. `B lt Al lt Ga lt In lt Tl`
C. `B lt Al lt In lt Ga lt Tl`
D. `B lt Ga lt Al lt In lt Tl`

Answer

To determine the correct order of atomic radii in group 13 elements, we will analyze the trends in atomic size as we move down the group from boron (B) to thallium (Tl).

### Step-by-Step Solution:

1. **Identify the Group 13 Elements**:
Group 13 elements include boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl).

2. **Understand the General Trend of Atomic Radii**:
- Atomic radii generally increase as we move down a group in the periodic table due to the addition of electron shells. Each element has more electron shells than the one above it, which increases the size of the atom.

3. **Consider the D-Block Contraction**:
- In the case of gallium (Ga), we need to consider the effect of d-block contraction. Gallium is located after the d-block elements, and the presence of d-electrons can lead to poor shielding of the nuclear charge. This results in a smaller atomic radius than expected.

4. **Compare Atomic Radii**:
- Boron (B) is the smallest due to having only two electron shells.
- Aluminum (Al) has a larger radius than boron but smaller than gallium.
- Gallium (Ga) is smaller than aluminum due to d-block contraction.
- Indium (In) has a larger radius than gallium because it has more electron shells.
- Thallium (Tl) has the largest atomic radius in this group, as it has the most electron shells.

5. **Establish the Order**:
Based on the above analysis, the order of atomic radii from smallest to largest is:
- **B < Ga < Al < In < Tl**

### Final Order of Atomic Radii:
The correct order of atomic radii in group 13 elements is:
**B < Ga < Al < In < Tl**