Which is not hydrolysed by water:

Options

A. `NCl_3`
B. `NF_3`
C. `PCl_3`
D. `BiCl_3`

Explanation

To determine which compound is not hydrolyzed by water, we need to analyze the compounds based on their ability to undergo hydrolysis. Hydrolysis typically requires the presence of a central atom that can develop a positive charge and has vacant d orbitals to accommodate the reaction with water.

### Step-by-Step Solution:

1. **Understanding Hydrolysis**:
Hydrolysis is a reaction where a compound reacts with water. For a compound to undergo hydrolysis, it generally needs to develop a positive charge and have vacant d orbitals.

2. **Analyzing the Given Compounds**:
- **NCl3 (Nitrogen Trichloride)**:
- Nitrogen is less electronegative than chlorine, leading to a partial positive charge on nitrogen.
- Chlorine has vacant d orbitals, allowing for hydrolysis to occur.
- **NF3 (Nitrogen Trifluoride)**:
- Here, nitrogen develops a positive charge, but nitrogen does not have vacant d orbitals.
- Therefore, NF3 cannot undergo hydrolysis.
- **PCl3 (Phosphorus Trichloride)**:
- Phosphorus can develop a positive charge and has vacant d orbitals.
- Thus, PCl3 can undergo hydrolysis.
- **BiCl3 (Bismuth Trichloride)**:
- Bismuth also has vacant d orbitals and can develop a positive charge.
- Therefore, BiCl3 can undergo hydrolysis.

3. **Conclusion**:
Based on the analysis, NF3 is the compound that cannot be hydrolyzed by water because nitrogen lacks vacant d orbitals necessary for the hydrolysis reaction.

### Final Answer:
**NF3 is not hydrolyzed by water.**