Which of the following trihalides is not hydrolysed

Options

A. `NF_3`
B. `NCl_3`
C. `PCl_3`
D. `AsCl_3`

Answer

To determine which of the following trihalides is not hydrolyzed, we will analyze each option based on the presence of vacant orbitals in the central atom and the ability of water to donate a lone pair to form hydrolysis products.

### Given Options:
1. NF3
2. NCl3
3. PCl3
4. AsCl3

### Step 1: Analyze NF3
- **Central Atom**: Nitrogen (N)
- **Electronic Configuration**: N has an atomic number of 7, with the configuration 1s² 2s² 2p³.
- **Vacant Orbitals**: Nitrogen does not have any d-orbitals. Therefore, it lacks vacant orbitals for hydrolysis.
- **Conclusion**: NF3 cannot undergo hydrolysis.

### Step 2: Analyze NCl3
- **Central Atom**: Nitrogen (N)
- **Electronic Configuration**: Same as above (1s² 2s² 2p³).
- **Vacant Orbitals**: Nitrogen still lacks d-orbitals, but chlorine (Cl) has vacant d-orbitals.
- **Hydrolysis Reaction**: NCl3 can hydrolyze to form ammonia (NH3) and hypochlorous acid (HOCl).
- **Conclusion**: NCl3 can undergo hydrolysis.

### Step 3: Analyze PCl3
- **Central Atom**: Phosphorus (P)
- **Electronic Configuration**: P has an atomic number of 15, with the configuration 1s² 2s² 2p⁶ 3s² 3p³.
- **Vacant Orbitals**: Phosphorus has empty 3d orbitals.
- **Hydrolysis Reaction**: PCl3 can hydrolyze to form phosphorous acid (H3PO3) and hydrochloric acid (HCl).
- **Conclusion**: PCl3 can undergo hydrolysis.

### Step 4: Analyze AsCl3
- **Central Atom**: Arsenic (As)
- **Electronic Configuration**: As has an atomic number of 33, with the configuration [Ar] 4s² 3d¹⁰ 4p³.
- **Vacant Orbitals**: Arsenic has empty 4d orbitals.
- **Hydrolysis Reaction**: AsCl3 can hydrolyze to form arsenous acid (H3AsO3) and hydrochloric acid (HCl).
- **Conclusion**: AsCl3 can undergo hydrolysis.

### Final Conclusion:
Based on the analysis, the only trihalide that does not hydrolyze is **NF3**.

### Answer:
**NF3 is the trihalide that is not hydrolyzed.**

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