When an alcohol is heated with excess of conc. `H_2 SO_4` at about `170^@`C, it gets dehydrated to form alkene(s). In this reaction, conc. `H_2 SO_4` acts as a dehydrating agent.
Which of the following statements is/are correct when 2-butanol undergoes dehydration?
I. Only one alkene having same number of carbon atoms as in 2-butanol is formed.
II. Two alkenes having different structural formulae but same molecular formula are formed. Only one alkene having one carbon atom less than 2- butanol is formed.
IV. Two alkenes are formed out of which one is terminal and other is non-terminal.
V. Two alkenes having the same percentage composition by mass are formed.

Options

A. II, IV and V only
B. III only
C. II and IV only
D. I only

Answer

To solve the question regarding the dehydration of 2-butanol when heated with concentrated sulfuric acid, let's analyze each statement step by step.

### Step 1: Understand the Reaction
When 2-butanol (C4H10O) is heated with concentrated sulfuric acid (H2SO4), it undergoes dehydration, which means it loses a water molecule (H2O) to form alkenes. The general reaction can be represented as:
\[ \text{C}_4\text{H}_{10}\text{O} \xrightarrow{\text{H}_2\text{SO}_4} \text{Alkene} + \text{H}_2\text{O} \]

### Step 2: Identify Possible Alkenes
2-butanol can lose a hydrogen atom from either of the two adjacent carbon atoms to the hydroxyl (-OH) group. This leads to the formation of two possible alkenes:
1. **But-2-ene** (non-terminal):
\[ \text{CH}_3\text{CH}=\text{CH}\text{CH}_3 \]
2. **But-1-ene** (terminal):
\[ \text{CH}_2=\text{CH}\text{CH}_2\text{CH}_3 \]

### Step 3: Evaluate Each Statement
Now, let's evaluate each statement provided in the question:

- **Statement I**: "Only one alkene having the same number of carbon atoms as in 2-butanol is formed."
- **Evaluation**: Incorrect. Two alkenes are formed (but-1-ene and but-2-ene).

- **Statement II**: "Two alkenes having different structural formulae but the same molecular formula are formed."
- **Evaluation**: Correct. Both but-1-ene and but-2-ene have the same molecular formula (C4H8) but different structural formulas.

- **Statement III**: "Only one alkene having one carbon atom less than 2-butanol is formed."
- **Evaluation**: Incorrect. Two alkenes are formed, not one with fewer carbon atoms.

- **Statement IV**: "Two alkenes are formed out of which one is terminal and the other is non-terminal."
- **Evaluation**: Correct. But-1-ene is terminal, and but-2-ene is non-terminal.

- **Statement V**: "Two alkenes having the same percentage composition by mass are formed."
- **Evaluation**: Correct. Both alkenes (but-1-ene and but-2-ene) have the same molecular formula (C4H8), hence the same percentage composition by mass.

### Conclusion
The correct statements are II, IV, and V.

### Final Answer
The correct options are: **II, IV, and V**.

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