In each of the following pairs of ions in which I ion is more stable than II

Options

A. `underset("I")(C_(6)H_(5)-overset(o+)CH_(2)) and underset("II")(CH_(2)=CH-overset(o+)CH_(2))`
B. `underset("I")(CH_(2))=overset(o+)CH and underset("II")(CH_(3))-overset(o+)CH_(2)`
C.
D. `underset("I")({:(CH_(3)-CH-CH_(3)),(" |"),(CH_(3)-underset(o+)C-CH_(3)):}) and underset("II")({:(CH_(3)-N-CH_(3)),(" |"),(CH_(3)-underset(o+)C-CH_(3)):})`

Answer

To determine which ion is more stable in each pair, we will analyze the stability of the given ions based on resonance, inductive effects, and the presence of lone pairs.

### Step-by-Step Solution:

1. **Analyzing the First Pair: C6H5CH2+ vs. CH2=CH2+**
- **C6H5CH2+ (Benzylic Carbocation)**: This carbocation is stabilized by resonance. The positive charge can be delocalized over the aromatic ring, allowing for multiple resonance structures.
- **CH2=CH2+ (Vinylic Carbocation)**: This carbocation is less stable because it does not have significant resonance stabilization. The positive charge is localized and cannot be delocalized effectively.
- **Conclusion**: C6H5CH2+ is more stable than CH2=CH2+.

2. **Analyzing the Second Pair: CH2=CH+ vs. CH3CH2+**
- **CH2=CH+ (Vinylic Carbocation)**: This carbocation is not stabilized by any alkyl groups and has limited resonance.
- **CH3CH2+ (Ethyl Carbocation)**: This carbocation is stabilized by the +I (inductive) effect from the adjacent alkyl group (ethyl group).
- **Conclusion**: CH3CH2+ is more stable than CH2=CH+.

3. **Analyzing the Third Pair: CH2=CH+ vs. CH2=CH-CH2+**
- **CH2=CH+ (Vinylic Carbocation)**: As previously mentioned, this carbocation has limited stabilization.
- **CH2=CH-CH2+ (Allylic Carbocation)**: This carbocation can be stabilized by resonance, as the positive charge can be delocalized over the adjacent double bond.
- **Conclusion**: CH2=CH-CH2+ is more stable than CH2=CH+.

4. **Analyzing the Fourth Pair: CH3C+(CH3)2 vs. CH3N+(CH3)2**
- **CH3C+(CH3)2 (Tertiary Carbocation)**: This carbocation is stabilized by the +I effect from the two methyl groups.
- **CH3N+(CH3)2 (Tertiary Ammonium Ion)**: The nitrogen has a lone pair that can stabilize the positive charge through back donation, which enhances stability.
- **Conclusion**: CH3N+(CH3)2 is more stable than CH3C+(CH3)2.

### Final Answer:
The only pair where the first ion is more stable than the second is the first pair: **C6H5CH2+ is more stable than CH2=CH2+.**