To determine the correct increasing order of trans-effect for the given species, we need to understand the concept of trans-effect in coordination chemistry, particularly in square planar complexes. The trans-effect refers to the influence of a ligand on the rate of substitution of another ligand that is positioned trans (opposite) to it.
### Step-by-Step Solution:
1. **Understanding Trans-Effect**:
- The trans-effect is the ability of a ligand to influence the substitution reaction of another ligand that is positioned trans to it in a square planar complex.
- Ligands can be classified based on their trans-effect strength, which can be influenced by their electronic properties (e.g., whether they are strong field ligands or pi-acceptors).
2. **Referencing the Trans-Effect Strength Table**:
- A commonly referenced order of trans-effect strength for various ligands is as follows:
- NO⁺ > CO > CN⁻ > C₂H₄ > C₆H₅ (phenyl) > NO₂ > I⁻ > SCN⁻ > Br⁻ > Cl⁻ > Py > NH₃ > OH⁻ > H₂O
- This table indicates that ligands like NO⁺ and CO have a strong trans-effect, while ligands like H₂O have a weak trans-effect.
3. **Analyzing the Given Options**:
- We need to compare the ligands in each option with the established trans-effect order.
- **Option 1**: NH₃, CN⁻, Br⁻, C₆H₅
- Incorrect: C₆H₅ should be after Br⁻.
- **Option 2**: CN⁻, C₆H₅, Br⁻, NH₃
- Correct: CN⁻ is stronger than C₆H₅, which is stronger than Br⁻, and NH₃ is the weakest among these.
- **Option 3**: Br⁻, CN⁻, NH₃, C₆H₅
- Incorrect: C₆H₅ should be before Br⁻.
- **Option 4**: CN⁻, Br⁻, C₆H₅, NH₃
- Incorrect: C₆H₅ should be before Br⁻.
4. **Conclusion**:
- The only option that reflects the correct increasing order of trans-effect is **Option 2**: CN⁻, C₆H₅, Br⁻, NH₃.
### Final Answer:
The correct increasing order of trans-effect of the given species is: **CN⁻ < C₆H₅ < Br⁻ < NH₃** (Option 2).
