In which of the following moleucles, all atoms are coplanar?

Options

A.
B.
C.
D.

Explanation

To determine which of the given molecules has all atoms coplanar, we need to analyze the hybridization of the carbon atoms in each molecule. Coplanarity means that all atoms lie in the same geometric plane.

### Step-by-Step Solution:

1. **Understand Coplanarity**:
- Coplanar molecules have all their atoms in the same plane. This is often associated with sp2 hybridization, where the bond angles are 120 degrees, allowing for a planar arrangement.

2. **Analyze Each Option**:
- **Option A**:
- The molecule consists of carbon atoms that are sp2 hybridized.
- In sp2 hybridization, the carbon atoms form a planar structure (like in alkenes).
- Therefore, all atoms in this molecule are coplanar.

- **Option B**:
- This molecule is cyclohexane, where each carbon atom is sp3 hybridized.
- In sp3 hybridization, the carbon atoms form a tetrahedral geometry, which means they are not coplanar.
- Thus, this molecule is not coplanar.

- **Option C**:
- This molecule contains carbon atoms that are sp2 hybridized (due to the double bond).
- However, it also has methyl groups attached to sp3 hybridized carbons.
- The presence of sp3 hybridized carbons means that not all atoms are in the same plane, making this molecule non-coplanar.

- **Option D**:
- Similar to option B, this molecule has carbon atoms that are sp3 hybridized.
- Therefore, it is also not coplanar.

3. **Conclusion**:
- After analyzing all options, the only molecule where all atoms are coplanar is **Option A**.

### Final Answer:
- The correct answer is **Option A**.