The best starting substrate to prepare `2-` Bromobenzoic acid is

Options

A.
B.
C.
D. None of these

Explanation

To determine the best starting substrate to prepare 2-Bromobenzoic acid, we need to analyze the options given and understand the effects of substituents on the aromatic ring.

### Step-by-Step Solution:

1. **Identify the Target Compound**: The target compound is 2-Bromobenzoic acid. This means we need to introduce a bromine atom at the 2-position of benzoic acid.

2. **Analyze the Substituents**:
- **Option A: Toluene (C6H5CH3)**: Toluene has a methyl group (-CH3) which is an electron-donating group (+I effect). Bromination of toluene will lead to substitution at the ortho (2-position) or para (4-position) due to the electron-donating nature of the methyl group. However, we need the bromine at the 2-position relative to the carboxylic acid group, which is not possible with toluene alone.

- **Option B: Para-Nitrotoluene (C6H4(NO2)(CH3))**: In this compound, the nitro group (-NO2) is a strong electron-withdrawing group (-M effect) and will direct electrophilic substitution to the meta position. However, the methyl group will still direct to the ortho and para positions. Since the para position is blocked by the nitro group, bromination will occur at the ortho position relative to the methyl group, leading to the formation of 2-bromobenzoic acid after oxidation.

- **Option C: Meta-Nitrotoluene (C6H4(NO2)(CH3))**: In this case, the nitro group will direct electrophilic substitution to the meta position. Bromination will occur at the meta position relative to the nitro group, which will not yield the desired 2-bromobenzoic acid.

- **Option D: None of the above**: This option suggests that none of the previous substrates are suitable, but we have already identified para-nitrotoluene as a viable option.

3. **Conclusion**: The best starting substrate to prepare 2-Bromobenzoic acid is **Para-Nitrotoluene (Option B)**. The nitro group will direct the bromination to the ortho position relative to the methyl group, which corresponds to the 2-position of benzoic acid after oxidation.

### Final Answer:
**Option B: Para-Nitrotoluene**