`3CH_(3)CHOunderset(298K)overset(H^(o+))rarrP`
Product P is a pleasant smelling liquid `( B.P. 410K).` . It is used
as a hypnotic. The structure of P is `:`

Options

A. `CH_(3)-CH=CH-CHO`
B.
C. `CH_(3)-underset(underset(OH)|)(C)H-CH_(2)-CHO`
D.

Answer

To solve the question regarding the reaction of acetaldehyde (CH₃CHO) in the presence of H⁺ at 298 K to form product P, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
We start with three molecules of acetaldehyde (CH₃CHO).

2. **Understand the Reaction Conditions**:
The reaction occurs in the presence of H⁺ ions (which can be provided by a strong acid like concentrated H₂SO₄) at a temperature of 298 K.

3. **Recognize the Type of Reaction**:
The reaction involves the condensation of acetaldehyde molecules. Under acidic conditions, acetaldehyde can undergo self-condensation to form a cyclic trimer.

4. **Draw the Structure of the Product**:
The condensation of three acetaldehyde molecules results in the formation of paraldehyde, which is a cyclic compound. The structure can be represented as:
- A six-membered ring with alternating carbon and oxygen atoms.
- Each carbon in the ring is bonded to a methyl group (CH₃).

5. **Confirm the Properties of Product P**:
- Paraldehyde is a pleasant-smelling liquid with a boiling point of approximately 410 K.
- It is known to be used as a hypnotic in medicine.

6. **Final Structure of Product P**:
The structure of paraldehyde can be represented as:
```
O
/ \
CH3 CH
| |
CH CH3
\ /
O
```
This cyclic structure confirms that the product P is paraldehyde.

### Conclusion:
The product P formed from the reaction of three molecules of acetaldehyde in the presence of H⁺ at 298 K is paraldehyde, which is a cyclic trimer of acetaldehyde.