Which of the following molecule is planar?

Options

A. `CH_4`
B. `C_2H_4`
C. NH_3
D. SiCl_4`

Answer

To determine which of the given molecules is planar, we will analyze each molecule based on its hybridization and geometry.

### Step-by-Step Solution:

1. **Identify the first molecule: CH₄ (Methane)**
- Carbon has 4 valence electrons.
- In CH₄, carbon forms 4 sigma bonds with 4 hydrogen atoms.
- **Steric Number**: 4 (4 sigma bonds + 0 lone pairs)
- **Hybridization**: sp³
- **Geometry**: Tetrahedral
- **Conclusion**: CH₄ is **not planar**.

2. **Identify the second molecule: C₂H₄ (Ethylene)**
- Each carbon has 4 valence electrons.
- In C₂H₄, each carbon forms 3 sigma bonds (2 with hydrogen and 1 with another carbon) and has a double bond between the two carbons.
- **Steric Number**: 3 (3 sigma bonds + 0 lone pairs)
- **Hybridization**: sp²
- **Geometry**: Trigonal planar
- **Conclusion**: C₂H₄ is **planar**.

3. **Identify the third molecule: NH₃ (Ammonia)**
- Nitrogen has 5 valence electrons.
- In NH₃, nitrogen forms 3 sigma bonds with 3 hydrogen atoms and has 1 lone pair.
- **Steric Number**: 4 (3 bond pairs + 1 lone pair)
- **Hybridization**: sp³
- **Geometry**: Trigonal pyramidal (due to the lone pair)
- **Conclusion**: NH₃ is **not planar**.

4. **Identify the fourth molecule: SiCl₄ (Silicon Tetrachloride)**
- Silicon has 4 valence electrons.
- In SiCl₄, silicon forms 4 sigma bonds with 4 chlorine atoms.
- **Steric Number**: 4 (4 sigma bonds + 0 lone pairs)
- **Hybridization**: sp³
- **Geometry**: Tetrahedral
- **Conclusion**: SiCl₄ is **not planar**.

### Final Conclusion:
Among the given molecules, **C₂H₄ (Ethylene)** is the only planar molecule.

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