Identify (X) in the following reaction
`CH_3-underset(OH)underset(|)CH-CH_2-overset(O)overset(||)CH overset(LiAlH_4)to X`

Answer

To identify (X) in the reaction of 3-hydroxybutanal with lithium aluminum hydride (LiAlH4), we will follow these steps:

### Step 1: Identify the Reactant
The reactant is 3-hydroxybutanal, which can be represented as:
- Structure:
```
CH3-CHOH-CH2-CHO
```
This compound has a hydroxyl (-OH) group and an aldehyde (C=O) functional group.

### Step 2: Understand the Role of LiAlH4
Lithium aluminum hydride (LiAlH4) is a strong reducing agent. It can reduce aldehydes and ketones to their corresponding alcohols. In this case, it will reduce the aldehyde group in 3-hydroxybutanal.

### Step 3: Mechanism of Reduction
1. **Nucleophilic Attack**: The hydride ion (H-) from LiAlH4 acts as a nucleophile and attacks the carbon atom of the carbonyl group (C=O) in the aldehyde.
2. **Formation of Alkoxide**: This attack leads to the formation of an alkoxide intermediate.
3. **Protonation**: Upon workup (usually with water), the alkoxide is protonated to form the final alcohol product.

### Step 4: Draw the Product
After the reduction, the structure of the product (X) will be:
- Structure:
```
CH3-CH(OH)-CH2-CH3
```
This compound is 3-butanol, which is a primary alcohol.

### Conclusion
Thus, the compound (X) formed from the reaction of 3-hydroxybutanal with LiAlH4 is **3-butanol**.