Stability of monovalent and trivalent cations of `Ga,In, Tl` lie in following sequence :

Options

A. `Tl lt ln gt Ga `
B. `ln lt Ga lt Tl `
C. `Ga lt ln lt Tl`
D. `Ga lt ln lt Tl `

Answer

To determine the stability of monovalent (M^+) and trivalent (M^3+) cations of Gallium (Ga), Indium (In), and Thallium (Tl), we will analyze the trends in Group 13 of the periodic table.

### Step-by-Step Solution:

1. **Understanding Group 13 Elements**:
- Group 13 consists of elements: Boron (B), Aluminium (Al), Gallium (Ga), Indium (In), and Thallium (Tl).
- The common oxidation states for these elements are +1 and +3.

2. **Stability of Monovalent Cations (M^+)**:
- The stability of the +1 oxidation state increases as we move down the group from Ga to In to Tl.
- This is due to the **inert pair effect**, which refers to the tendency of the s-electrons (the 'inert pair') to remain non-bonding and not participate in bonding as we go down the group.
- Thus, the order of stability for monovalent cations is:
\[ \text{Tl}^+ > \text{In}^+ > \text{Ga}^+ \]

3. **Stability of Trivalent Cations (M^3+)**:
- In contrast, the stability of the +3 oxidation state decreases as we move down the group.
- The inert pair effect is more pronounced in heavier elements like Tl, making it less stable in the +3 oxidation state compared to Ga and In.
- Therefore, the order of stability for trivalent cations is:
\[ \text{Ga}^{3+} > \text{In}^{3+} > \text{Tl}^{3+} \]

4. **Final Summary of Stability Orders**:
- For monovalent cations:
\[ \text{Tl}^+ > \text{In}^+ > \text{Ga}^+ \]
- For trivalent cations:
\[ \text{Ga}^{3+} > \text{In}^{3+} > \text{Tl}^{3+} \]

### Conclusion:
The stability of the cations can be summarized as:
- **Monovalent**: Tl^+ > In^+ > Ga^+
- **Trivalent**: Ga^3+ > In^3+ > Tl^3+