Go though the following statements
(i) Meselson & stahl used cesium chloride density gradient to distinguish heavy DNA molecules from the normal DNA molecules.
(ii) In meselson & Stahl experiment the DNA that was extracted from the culture one generation after the transfer from `.^(15)N` to `.^(14)N`, was composed of equal amount of hybrid (intermediate) DNA and of light DNA.
(iii) In prokaryotes, control the rate of transcriptional initiation is the predominant site for control of gene expression.
(iv) In lac operon, the repressor is synthesised only at the time when the level of metabolite is in excess.
Find out the correct statements?

Options

A. (i) & (iii)
B. (ii) & (iv)
C. (i), (iii) & (iv)
D. (ii), (iii) & (iv)

Explanation

To determine the correct statements from the provided options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement (i):** "Meselson & Stahl used cesium chloride density gradient to distinguish heavy DNA molecules from the normal DNA molecules."
- **Analysis:** This statement is correct. Meselson and Stahl conducted their famous experiment using cesium chloride density gradient centrifugation to separate DNA based on density. They distinguished between heavy DNA (labeled with nitrogen-15) and light DNA (labeled with nitrogen-14).

2. **Statement (ii):** "In Meselson & Stahl experiment the DNA that was extracted from the culture one generation after the transfer from ^(15)N to ^(14)N, was composed of equal amount of hybrid (intermediate) DNA and of light DNA."
- **Analysis:** This statement is incorrect. After one generation in the presence of ^(14)N, the DNA consists of hybrid DNA (one strand of ^(15)N and one strand of ^(14)N) only. There would not be an equal amount of hybrid and light DNA; the light DNA would only appear after the second generation.

3. **Statement (iii):** "In prokaryotes, control the rate of transcriptional initiation is the predominant site for control of gene expression."
- **Analysis:** This statement is correct. In prokaryotes, the initiation of transcription is indeed the primary regulatory point for gene expression. This is where the RNA polymerase binds to the promoter and starts transcription.

4. **Statement (iv):** "In lac operon, the repressor is synthesised only at the time when the level of metabolite is in excess."
- **Analysis:** This statement is incorrect. In the lac operon, the repressor is synthesized continuously, regardless of the metabolite levels. It binds to the operator region to inhibit transcription unless lactose is present, which inactivates the repressor.

### Conclusion:
The correct statements are:
- Statement (i) is correct.
- Statement (iii) is correct.

Thus, the correct answer is **Statements (i) and (iii)**.