Acetylene on heating in the presence of red hot Fe tube gives :

Options

A. Benzene
B. Cyclooctatetraene
C. naphthalene
D. Anthracene

Answer

To solve the question regarding what acetylene (ethyne) produces when heated in the presence of a red hot iron tube, we can follow these steps:

### Step 1: Identify the Structure of Acetylene
Acetylene, also known as ethyne, has the chemical formula C₂H₂. Its structure can be represented as H-C≡C-H, where there is a triple bond between the two carbon atoms.

**Hint:** Remember that acetylene is a simple alkyne with a triple bond between two carbon atoms.

### Step 2: Understand the Reaction Conditions
The question specifies that acetylene is heated in the presence of a red hot iron tube. The temperature is typically around 873 Kelvin. Under these conditions, acetylene can undergo a reaction known as polymerization.

**Hint:** Heating acetylene can lead to various reactions, including polymerization, especially in the presence of a catalyst like iron.

### Step 3: Describe the Polymerization Process
When acetylene is heated, it can trimerize, meaning three molecules of acetylene can combine to form a larger molecule. In this case, the trimerization of acetylene leads to the formation of a cyclic structure.

**Hint:** Trimerization involves the combination of three monomer units to form a polymer.

### Step 4: Determine the Product of the Reaction
The trimerization of acetylene results in the formation of benzene (C₆H₆). The reaction can be summarized as three acetylene molecules combining to form one benzene molecule.

**Hint:** Benzene is a cyclic compound with alternating double bonds, which can be formed from the trimerization of acetylene.

### Step 5: Write the Overall Reaction
The overall reaction can be represented as:
\[ 3 \text{C}_2\text{H}_2 \xrightarrow{\text{red hot Fe}} \text{C}_6\text{H}_6 \]

This indicates that three molecules of acetylene yield one molecule of benzene when heated in the presence of red hot iron.

**Hint:** Always balance the chemical equation to ensure that the number of atoms on both sides is equal.

### Final Answer
When acetylene is heated in the presence of a red hot iron tube, it gives benzene.

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