Which one of the following molecules is planar?

Options

A. `NH_(3)`
B. `NCI_(3)`
C. `PH_(3)`
D. `BF_(3)`

Explanation

To determine which of the given molecules is planar, we will analyze the molecular geometry of each molecule mentioned in the question.

### Step-by-Step Solution:

1. **Identify the Molecules**: The molecules we need to analyze are NH3 (ammonia), NCl3 (nitrogen trichloride), PS3 (phosphorus trisulfide), and BF3 (boron trifluoride).

2. **Analyze NH3 (Ammonia)**:
- Ammonia has a trigonal pyramidal structure due to the presence of a lone pair on the nitrogen atom.
- This lone pair causes the molecule to adopt a three-dimensional shape, making it non-planar.

3. **Analyze NCl3 (Nitrogen Trichloride)**:
- Similar to ammonia, nitrogen trichloride also has a trigonal pyramidal structure.
- The presence of a lone pair on nitrogen leads to a non-planar arrangement.

4. **Analyze PS3 (Phosphorus Trisulfide)**:
- Phosphorus trisulfide has a similar structure to ammonia and nitrogen trichloride, which is also trigonal pyramidal.
- Thus, PS3 is also non-planar.

5. **Analyze BF3 (Boron Trifluoride)**:
- Boron trifluoride has a trigonal planar structure.
- All three fluorine atoms are located in the same plane around the boron atom, making BF3 a planar molecule.

6. **Conclusion**:
- Among the given molecules, only BF3 is planar. Therefore, the correct answer is BF3.

### Answer:
The planar molecule among the given options is **BF3**.

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