Observe the following two reactions:
(I). `CH_(3)-underset(O)underset(||)C-CH+C_(2)H_(5)overset(18)Hoverset(H_(2)SO_(4))to"products"+"water"`
(II). `(X)+"water"overset(("sodium hydroxide")/(Delta))toCH_(3)-underset(O)underset(||)(C)-overset(18)(O)Na+C_(2)H_(5)OH`
the correct statements are:

Options

A. In reaction(I) the products is `CH_(3)-underset(O)underset(||)C-overset(18)O-C_(2)H_(5)`
B. In reaction (II) the reactant is `CH_(3)-underset(O)underset(||)C-overset(18)C-C_(2)H_(5)`
C. In reaction (II) the reagent is `(H_(2)overset(18))/(Naoverset(18)OH)`
D. Reaction (I) is irreversible while reaction (II) is reversible.

Explanation

To solve the question regarding the two reactions provided, we will analyze each reaction step by step.

### Step 1: Analyze Reaction I
The first reaction is represented as:
\[ \text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{H}_2\text{SO}_4} \text{Products} + \text{H}_2\text{O} \]

1. **Identify the reactants**: The reactants are acetic acid (\( \text{CH}_3\text{COOH} \)) and ethanol (\( \text{C}_2\text{H}_5\text{OH} \)).
2. **Determine the type of reaction**: This is an esterification reaction where an acid and an alcohol react to form an ester and water.
3. **Identify the product**: The product formed is ethyl acetate (\( \text{CH}_3\text{COOC}_2\text{H}_5 \)) along with water.

### Step 2: Analyze Reaction II
The second reaction is represented as:
\[ (X) + \text{H}_2\text{O} \xrightarrow{\text{NaOH}/\Delta} \text{CH}_3\text{COONa} + \text{C}_2\text{H}_5\text{OH} \]

1. **Identify the reactant**: Here, \( X \) is the product from the first reaction, which is ethyl acetate (\( \text{CH}_3\text{COOC}_2\text{H}_5 \)).
2. **Determine the type of reaction**: This is a hydrolysis reaction, specifically basic hydrolysis, where the ester reacts with water in the presence of sodium hydroxide to form a sodium salt of the acid (sodium acetate) and ethanol.
3. **Identify the products**: The products are sodium acetate (\( \text{CH}_3\text{COONa} \)) and ethanol (\( \text{C}_2\text{H}_5\text{OH} \)).

### Step 3: Evaluate the Statements
Now we will evaluate the correctness of the statements provided in the question:

1. **Statement A**: In reaction 1, the product is \( \text{CH}_3\text{COOC}_2\text{H}_5 \) (Ethyl acetate).
- **Correct**: This is true as established in Step 1.

2. **Statement B**: In reaction 2, the reactant is \( \text{CH}_3\text{COOC}_2\text{H}_5 \).
- **Correct**: This is true as established in Step 2.

3. **Statement C**: In reaction 2, the reagent is \( \text{H}_2\text{O} \) and \( \text{NaOH} \).
- **Incorrect**: The statement mentions "hydrogen 18 or NaOH 18," which is misleading. The reagent is sodium hydroxide (NaOH) and water, but oxygen-18 is not a reagent here.

4. **Statement D**: Reaction 1 is irreversible and reaction 2 is reversible.
- **Incorrect**: Reaction 1 (esterification) is reversible, while reaction 2 (basic hydrolysis of the ester) is irreversible.

### Final Conclusion
The correct statements are:
- Statement A and Statement B are correct.