The correct decreasing order of `1^st` ionizationenergy of 13-group elements is

Options

A. `BgtAlgtGagtIngtTl`
B. BgtTlgtGagtAlgtIn
C. BgtGagtAlgtTlgtIn
D. AlgtBgtGagtIngtTl

Answer

To determine the correct decreasing order of the first ionization energy of Group 13 elements, we will analyze the elements in this group and their respective ionization energies.

### Step-by-Step Solution:

1. **Identify the Group 13 Elements**:
The elements in Group 13 of the periodic table are Boron (B), Aluminum (Al), Gallium (Ga), Indium (In), and Thallium (Tl).

2. **Understand Ionization Energy**:
Ionization energy is the energy required to remove an electron from an isolated gaseous atom. Generally, ionization energy increases across a period and decreases down a group.

3. **Consider the Trends in Ionization Energy**:
- **Across a Period**: Ionization energy increases due to increased nuclear charge and decreased atomic radius, which leads to electrons being held more tightly.
- **Down a Group**: Ionization energy generally decreases due to increased atomic size and shielding effect, which makes it easier to remove an outer electron.

4. **Analyze Each Element**:
- **Boron (B)**: Has the highest ionization energy due to its small atomic size and effective nuclear charge.
- **Thallium (Tl)**: Although it is lower in the group, it has a higher ionization energy than Ga and Al because it follows the d-block and f-block elements, which have poor shielding, resulting in a stronger attraction of the nucleus on the valence electrons.
- **Gallium (Ga)**: Has a higher ionization energy than Al due to the presence of d-block electrons which provide poor shielding.
- **Aluminum (Al)**: Has a lower ionization energy than Ga due to its larger atomic size and increased shielding effect.
- **Indium (In)**: Has the lowest ionization energy in this group due to its larger atomic size and increased shielding effect.

5. **Establish the Correct Order**:
Based on the analysis above, the correct decreasing order of first ionization energy for Group 13 elements is:
\[ \text{B} > \text{Tl} > \text{Ga} > \text{Al} > \text{In} \]

### Final Answer:
The correct decreasing order of first ionization energy of Group 13 elements is:
\[ \text{Boron (B)} > \text{Thallium (Tl)} > \text{Gallium (Ga)} > \text{Aluminum (Al)} > \text{Indium (In)} \]