Which of the statements is/are correct ?

Options

A. In Reformatsky reaction, `alpha-bromo` ester reacts with aldehyde or ketone in the presence of `Mg` to give `beta-hydroxy` ester.
B. In Reformatsky reaction, `alpha-bromo` ester reacts with aldehyde or ketone in the presence of `Zn` to give `beta-hydroxy` ester.
C. Citric acid is prepared by the reaction of `alpha-bromoethyl` acetate and ethyl oxaloacetate in the presence of `Zn` followed by hydrolysis.
D. Citric acid is prepared by the fermentation of molasses in the presence of Aspergillus wentienzymes.

Answer

To determine which statements regarding the reactions involving Grignard reagents and organometallic reagents are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze Statement 1**:
- The statement claims that in the Reformatzky reaction, an alpha-bromo ester reacts with an aldehyde or ketone in the presence of magnesium to give a beta-hydroxy ester.
- **Evaluation**: This statement is incorrect because the Reformatzky reaction typically involves zinc as the metal, not magnesium. Therefore, this statement does not accurately describe the reaction.

2. **Analyze Statement 2**:
- This statement is similar to the first but states that the reaction occurs in the presence of zinc.
- **Evaluation**: This statement is correct. The Reformatzky reaction involves the reaction of an alpha-bromo ester with an aldehyde or ketone in the presence of zinc, resulting in the formation of a beta-hydroxy ester.

3. **Analyze Statement 3**:
- The statement claims that citric acid is prepared by the reaction of alpha-bromomethyl acetate and ethyl oxoacetate in the presence of zinc, followed by hydrolysis.
- **Evaluation**: This statement is correct. The reaction of alpha-bromomethyl acetate with ethyl oxoacetate in the presence of zinc indeed leads to the formation of citric acid after hydrolysis.

4. **Analyze Statement 4**:
- This statement claims that citric acid is prepared by the fermentation of molasses in the presence of the Aspergillus enzyme.
- **Evaluation**: This statement is also correct. Citric acid can be produced through the fermentation of molasses using specific microorganisms, including Aspergillus species.

### Conclusion:
- **Correct Statements**:
- Statement 2: Correct
- Statement 3: Correct
- Statement 4: Correct
- **Incorrect Statement**:
- Statement 1: Incorrect

Thus, the correct statements are 2, 3, and 4.