How many toluidines on reaction with `NaNO_(2)//HCl` followed by `H_(3)PO_(2)` treatment gives Toluene.

Answer

To solve the question of how many toluidines react with `NaNO2/HCl` followed by `H3PO2` to yield toluene, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Structures of Toluidines**:
- There are three isomers of toluidine: ortho-toluidine, meta-toluidine, and para-toluidine.
- The structures are:
- Ortho-toluidine: NH2 at the ortho position to the methyl group (CH3).
- Meta-toluidine: NH2 at the meta position to the methyl group (CH3).
- Para-toluidine: NH2 at the para position to the methyl group (CH3).

2. **Reaction with NaNO2/HCl**:
- All three toluidines will undergo diazotization when treated with sodium nitrite (NaNO2) in hydrochloric acid (HCl).
- This reaction converts the amine group (NH2) into a diazonium salt (N2+Cl-).

3. **Treatment with H3PO2**:
- The diazonium salt formed from each toluidine will then react with phosphorous acid (H3PO2).
- This reaction leads to the substitution of the diazonium group (N2+) with a hydrogen atom, resulting in the formation of toluene (C6H5-CH3).

4. **Determine Which Toluidines Yield Toluene**:
- **Ortho-toluidine**:
- Forms a diazonium salt and upon treatment with H3PO2, it yields toluene.
- **Meta-toluidine**:
- Also forms a diazonium salt, and similarly, after treatment with H3PO2, it yields toluene.
- **Para-toluidine**:
- Forms a diazonium salt as well, and upon treatment with H3PO2, it also yields toluene.

5. **Conclusion**:
- All three isomers of toluidine (ortho, meta, and para) can be converted into toluene through the described reactions.
- Therefore, the answer to the question is **three**.

### Summary:
The three toluidines that can react with `NaNO2/HCl` followed by `H3PO2` to give toluene are ortho-toluidine, meta-toluidine, and para-toluidine.