The correct option is "The normal DNA from ¹⁵N-DNA".

Step-by-Step Explanation:

1. Context of the Experiment:
Matthew Meselson and Franklin Stahl performed their famous experiment in 1958 to prove the semi-conservative replication of DNA using the bacterium Escherichia coli (E. coli).

2. Use of Nitrogen Isotopes:
They grew E. coli in a medium containing a heavy isotope of nitrogen, ¹⁵N (in the form of ¹⁵NH₄Cl), as the sole nitrogen source for many generations. This resulted in the incorporation of ¹⁵N into the newly synthesized DNA, making it "heavy" DNA. They then transferred the cells to a medium containing the normal light isotope, ¹⁴N (in the form of ¹⁴NH₄Cl).

3. Cesium Chloride (CsCl) Density Gradient Centrifugation:
To distinguish between the DNA containing the normal light isotope (¹⁴N-DNA) and the DNA containing the heavy isotope (¹⁵N-DNA), they extracted DNA from the bacterial cells at various time intervals and subjected it to density gradient centrifugation using cesium chloride (CsCl).

4. Separation Mechanism:
When CsCl is centrifuged at very high speeds, it forms a density gradient where the density increases from the top to the bottom of the centrifuge tube. During centrifugation, the DNA molecules migrate to a position in the gradient where their density matches the density of the surrounding CsCl solution. Because ¹⁵N-DNA has a higher density than normal ¹⁴N-DNA, the two types of DNA sediment at different levels in the gradient, allowing them to be separated based on their density differences.