In which of the following molecules all the atoms lie in one plane ? .

Options

A. `CO_(2)`
B. `BF_(3)`
C. `PF_(5)`
D. `NH_(3)`

Explanation

To determine which of the given molecules has all its atoms lying in one plane, we will analyze the molecular geometry of each option provided.

### Step-by-Step Solution:

1. **Analyze Carbon Dioxide (CO₂)**:
- The molecular structure of CO₂ is linear.
- In a linear molecule, all atoms lie in the same plane.
- Therefore, CO₂ is planar.
- **Conclusion**: CO₂ is a correct option.

2. **Analyze Boron Trifluoride (BF₃)**:
- The molecular structure of BF₃ is trigonal planar.
- In a trigonal planar molecule, all three atoms bonded to the central atom (Boron) lie in the same plane.
- Therefore, BF₃ is planar.
- **Conclusion**: BF₃ is also a correct option.

3. **Analyze Phosphorus Pentafluoride (PF₅)**:
- The molecular structure of PF₅ is trigonal bipyramidal.
- In this structure, while three fluorine atoms are in one plane, the other two fluorine atoms are positioned above and below this plane.
- Therefore, PF₅ is not planar.
- **Conclusion**: PF₅ is an incorrect option.

4. **Analyze Ammonia (NH₃)**:
- The molecular structure of NH₃ is pyramidal.
- In a pyramidal structure, the nitrogen atom is at the apex and the three hydrogen atoms form a base that is not in the same plane as the nitrogen.
- Therefore, NH₃ is not planar.
- **Conclusion**: NH₃ is also an incorrect option.

### Final Answer:
The molecules in which all the atoms lie in one plane are **Carbon Dioxide (CO₂)** and **Boron Trifluoride (BF₃)**.