Which of the following reagents on treatment with benzenamine in basic medium produces phynyl isocyanide?

Options

A. `C Cl_4`
B. Trichloromethane
C. Methylene dichloride
D. Hexachloroethane

Explanation

To solve the question of which reagent, when treated with benzenamine in a basic medium, produces phenyl isocyanate, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The main reactant is benzenamine, which can be represented as PhNH2 (where Ph stands for the phenyl group, C6H5).
- We need to identify the correct reagent from the options provided: A) CCl4, B) CHCl3 (trichloromethane), C) methylene dichloride, D) hexachloroethane.

2. **Understand the Reaction**:
- The reaction we are interested in is the formation of isocyanates from primary amines. The general reaction for this is:
\[ RNH2 + KOH + CHCl3 \rightarrow RNC + KCl + H2O \]
- Here, R represents the organic group (in this case, the phenyl group from benzenamine).

3. **Identify the Correct Reagent**:
- The reagent that is commonly used to produce isocyanates from primary amines in the presence of a strong base (like KOH) is trichloromethane (CHCl3).
- Other reagents listed (CCl4, methylene dichloride, hexachloroethane) do not typically participate in this reaction to form isocyanates.

4. **Write the Reaction Equation**:
- The specific reaction for benzenamine with KOH and trichloromethane can be written as:
\[ \text{PhNH}_2 + \text{KOH} + \text{CHCl}_3 \rightarrow \text{PhNCO} + \text{KCl} + \text{H}_2\text{O} \]
- This confirms that phenyl isocyanate (PhNCO) is produced.

5. **Conclusion**:
- Therefore, the correct answer is option B) CHCl3 (trichloromethane).

### Final Answer:
The reagent that, when treated with benzenamine in basic medium, produces phenyl isocyanate is **B) CHCl3 (trichloromethane)**.