The ionisation energies from Ga to TI do not decrease due to

Options

A. Shielding effect
B. Improper shielding effect
C. Increase in atomic size
D. Decrease in nuclear charge

Answer

To solve the question regarding why the ionization energies from Gallium (Ga) to Thallium (Tl) do not decrease, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Ionization Energy**:
- Ionization energy is the minimum energy required to remove an electron from an isolated gaseous atom. It generally decreases down a group in the periodic table due to increased atomic size and shielding effect.

2. **Identifying the Elements**:
- Gallium (Ga) and Thallium (Tl) are both elements in Group 13 of the periodic table. We need to analyze the trend in ionization energy from Ga to Tl.

3. **Analyzing the Trend**:
- Typically, as we move down a group in the periodic table, the ionization energy decreases because the outermost electrons are further from the nucleus and are shielded by inner electrons.

4. **Considering the Shielding Effect**:
- The shielding effect refers to the phenomenon where inner shell electrons shield the outer shell electrons from the full effect of the nucleus's positive charge. In the case of Ga to Tl, the presence of d and f orbitals contributes to poor shielding.

5. **Impact of Nuclear Charge**:
- While the nuclear charge (the total positive charge of the nucleus) increases as we move from Ga to Tl, the poor shielding effect means that the outermost electrons do not experience a significant reduction in effective nuclear charge.

6. **Conclusion**:
- Due to the improper shielding effect from the d and f orbitals, the ionization energy does not decrease as expected. Instead, it remains relatively constant or may even increase slightly.

### Final Answer:
The ionization energies from Ga to Tl do not decrease due to the **improper shielding effect**.