The correct option is (iii) → (iv) → (i) → (ii) → (v).

To understand why this sequence is correct, let us break down the steps of the famous Meselson and Stahl experiment (1958) which proved the semi-conservative nature of DNA replication:

Step 1: Growing Bacteria in Heavy Nitrogen (iii)
Meselson and Stahl first grew Escherichia coli (bacteria) in a medium containing ammonium chloride (${\text{NH}}_4^{\text{Cl}}$) labeled with the heavy isotope of nitrogen, $15\text{N}$, as the sole nitrogen source for many generations.

Step 2: Incorporating Heavy Nitrogen into DNA (iv)
Because the bacteria were grown in the $15\text{N}$ medium for many generations, the heavy isotope was incorporated into the newly synthesized DNA of all the bacteria. As a result, all bacteria contained heavy DNA ($15\text{N}$ DNA).

Step 3: Transferring to Light Nitrogen Medium (i)
Next, they transferred these bacteria with fully labeled $15\text{N}$ DNA into a medium containing normal, light nitrogen ($14\text{N}$). They took samples at regular generation intervals, specifically every 20 minutes (which is the replication time for E. coli).

Step 4: Formation of Hybrid DNA (ii)
DNA isolated from the cells after one generation of transfer (at 20 minutes) was extracted and analyzed using cesium chloride (CsCl) density gradient centrifugation. It was found that all the bacteria contained hybrid DNA consisting of one strand of $14\text{N}$ DNA and one strand of $15\text{N}$ DNA. This showed that replication was semi-conservative.

Step 5: Subsequent Generations (v)
After the second generation (40 minutes), the DNA extracted from the culture was composed of equal amounts of this hybrid DNA ($14\text{N}$-$15\text{N}$) and light DNA ($14\text{N}$-$14\text{N}$). Thus, the bacteria contained either all light $14\text{N}$ DNA or hybrid DNA.

Aligning these events sequentially gives the correct order: (iii) → (iv) → (i) → (ii) → (v).