`C_6H_6underset(H_2SO_4)overset(HNO_3)rarrXunderset(FeCl_3)overset(Cl_2)rarrY`
Sequence Y can be

Options

A. 3-nitrochlorobenzene
B. 1-nitrochlorobenzene
C. 4-nitrochlorobenzene
D. none of these

Explanation

To solve the problem step by step, we will analyze the reactions taking place and the products formed.

### Step 1: Identify the starting compound
The starting compound is benzene, which has the molecular formula \( C_6H_6 \).

### Step 2: Nitration of Benzene
When benzene is treated with a mixture of concentrated sulfuric acid (\( H_2SO_4 \)) and nitric acid (\( HNO_3 \)), a nitration reaction occurs. The nitric acid generates the nitronium ion (\( NO_2^+ \)), which acts as an electrophile.

**Reaction:**
\[ C_6H_6 + HNO_3 \xrightarrow{H_2SO_4} C_6H_5NO_2 + H_2O \]
This reaction leads to the formation of nitrobenzene (\( C_6H_5NO_2 \)), which we will denote as product \( X \).

### Step 3: Chlorination of Nitrobenzene
Next, nitrobenzene (\( X \)) is treated with chlorine (\( Cl_2 \)) in the presence of iron(III) chloride (\( FeCl_3 \)). This setup facilitates a chlorination reaction.

**Key Concept:**
The nitro group (\( NO_2 \)) is an electron-withdrawing group and directs incoming substituents to the meta position due to its deactivating effect on the benzene ring.

**Reaction:**
\[ C_6H_5NO_2 + Cl_2 \xrightarrow{FeCl_3} C_6H_4ClNO_2 \]
Since the nitro group directs substitution to the meta position, the chlorine will be added to the meta position relative to the nitro group.

### Step 4: Identify the final product
The final product \( Y \) will be 3-Nitrochlorobenzene, which can be represented as:
\[ \text{3-Nitrochlorobenzene} \quad (C_6H_4ClNO_2) \]

### Conclusion
The sequence \( Y \) can be identified as **3-Nitrochlorobenzene**.