According to VSEPR theory, in which species do all the atoms lie in the same plane ?
`1. CH_(3)^(+) " " 2. CH_(3)^(-)`

Options

A. 1 only
B. 2 only
C. both 1 and 2
D. neither 1 nor 2

Explanation

To determine which of the given species has all atoms lying in the same plane according to VSEPR theory, we will analyze the structures of CH₃⁺ (methyl cation) and CH₃⁻ (methyl anion).

### Step-by-Step Solution:

1. **Identify the Valence Electrons:**
- Carbon (C) is in group 14 and has 4 valence electrons.
- For CH₃⁺, the positive charge means it has lost one electron, leaving it with 3 valence electrons.
- For CH₃⁻, the negative charge means it has gained one electron, giving it 5 valence electrons.

2. **Draw the Lewis Structures:**
- **For CH₃⁺:**
- Carbon is bonded to three hydrogen atoms.
- The structure will show carbon at the center with three hydrogen atoms around it.
- There are no lone pairs on the carbon atom.
- **For CH₃⁻:**
- Carbon is bonded to three hydrogen atoms and has one lone pair.
- The structure will show carbon at the center with three hydrogen atoms and a lone pair above or below the carbon.

3. **Calculate the Steric Number:**
- **For CH₃⁺:**
- Steric number = Number of sigma bonds + Number of lone pairs = 3 sigma bonds + 0 lone pairs = 3.
- **For CH₃⁻:**
- Steric number = 3 sigma bonds + 1 lone pair = 4.

4. **Determine Hybridization:**
- **For CH₃⁺:**
- With a steric number of 3, the hybridization is sp².
- **For CH₃⁻:**
- With a steric number of 4, the hybridization is sp³.

5. **Identify the Geometry:**
- **For CH₃⁺:**
- The geometry is trigonal planar, which means all atoms (C and H) lie in the same plane.
- **For CH₃⁻:**
- The geometry is trigonal pyramidal due to the presence of the lone pair, which means not all atoms lie in the same plane.

### Conclusion:
- **CH₃⁺ (methyl cation)** has all its atoms in the same plane (trigonal planar).
- **CH₃⁻ (methyl anion)** does not have all its atoms in the same plane due to the lone pair (trigonal pyramidal).

Thus, the answer is **1. CH₃⁺**.